It is characteristic of the work of a really great genius, either in Science, Literature or Art, that it is not displaced and cannot be displaced by that which may come after it.

A bit of scientific work may later be found to be erroneous as to data, and, therefore, in the wrong as to conclusions, but if it be the work of an aggressive, original thinker, it will always have great value. In the brilliant galaxy of physicists, or, as he would himself call them, natural philosophers, which the present century has produced, it is moderation to say that none outshines Lord Kelvin, and it will not be denied that none has equalled him in aggressiveness and originality. The range of subjects upon which he has touched during his long and active life is so extensive as to certainly justify the use of the term Natural Philosopher in its broader sense (and capitalized at that), for he has never touched a department of human knowledge without leaving it richer and more extensive for his contact with it. That he has not been invariably infallible is recognized by no one more fully than by himself, and the new editions of his earlier papers which have been issuing from the press at intervals during the past few years, bear most interesting evidence of his readiness to change his attitude on great questions whenever the verdict of later investigations is against him. It is delightful to note the occasional parenthetical'not' put to-day into a sentence which twenty years ago declared very positively that there is so and so, or, can,' etc., completely reversing the meaning of statements which were once made with a good degree of confidence. Whatever else may be said, it cannot be asserted that Lord Kelvin has ever lacked the courage to express his own views in most forcible and unmistakable language. Indeed, in this respect, especially, he has set a splendid standard of unswerving scientific honesty

6

we

for the innumerable workers who have been, and will be, more or less influenced by his methods and their tremendous productiveness.

His views as to the proper attitude of the philosopher in his relations to unexplored regions of human experience are concisely expressed in this noble sentence from his Presidential Address before the British Association for the Advancement of Science, in 1871 "Science is bound by the everlasting law of honor to face fearlessly every problem which can fairly be presented to it." When he comes, however, to touch upon some problems which have long been of great interest to the human race, but which have been assumed, usually, to lie outside the domain of experimental or exact science (and he touches upon them not infrequently in the volume under consideration), it is not difficult to see a very decided bias towards certain views, and a promptness to accept propositions not always well supported by evidence, very greatly in contrast with what is found in more vigorously scientific discussion.

This series of popular lectures and addresses is published in three volumes, the first and third having already appeared. The second (issued later than the third), to which attention is now invited, contains the important addresses on geological physics which have attracted so much attention during the past quarter of a century, together with a number of lectures and short papers on subjects related to general physics and extracts from addresses as president of the Royal Society since 1890. The geological papers are of great interest and have had much to do with the moulding of the views of geologists as to Dynamical Geology. The series begins with a short note covering but a single octavo page, entitled, The Doctrine of Uniformity in Geology Briefly Refuted,' read at Edinburgh in 1865. It fairly opens the ball,' and may be regard

6

ed as the key note to the more elaborate disquisitions which followed at intervals up to recent dates. These papers are so well known, or ought to be so well known, to all geologists as to make it only necessary to say here that they will be found collected in this volume in convenient form and with a few notes and occasional comments by the distinguished author, made while the collection was being prepared for the press. The most important of the earlier papers are the address On Geological Time,' given in Glasgow, early in 1868, and that on 'Geological Dynamics' at the same place about a year later. In the first of these will be found the somewhat severe strictures upon 'British Popular Geology' which brought forth the interesting and pointed criticisms of Huxley in his address to the Geological Society of London, and in the second the replies to Huxley's criticisms and futher remarks upon the subject. Nearly ten years later came a 'Review of the Evidence Regarding the Physical Condition of the Earth,' read at the British Association meeting at Glasgow; two papers read before the Geological Society of Glasgow, on 'Geological Climate,' and on the Internal Condition of the Earth;' and after the lapse of another ten years a paper before the same society on 'Polar Ice Caps and their Influence in Changing Sea Levels.' In these much of the ground of the earlier addresses is again gone over, in the light of later discovery in geology, physics and astronomy.

Indeed these same topics recur again and again, sometimes incidentally in other addresses in the volume, and Lord Kelvin makes it entirely clear that in thus taking up the discussion of geological problems and applying to them the methods and data of physics and astronomy, he does not wish to be considered an interloper. In his reply to Huxley, who had rather pointedly intimated that view of the situation, he good-naturedly remarks: "For myself I am anxious to be regarded by geologists,

not as a mere passer-by, but as one constantly interested in their grand subject, and anxious in any way, however slight, to assist them in their search for truth.”

It seems difficult to over-estimate the importance of these geological addresses, not only to the geologist, but to the physicist as well. They not only have a general interest to both, but are of special importance to each. To the one they open new possibilities of a somewhat exact and satisfactory treatment of a most important but hitherto rather unmanageable department of his subject; and to the other they offer a most instructive illustration of the power and scope of the methods of exact science, when applied by one who may justly be called not a master, but the master.

Of the other addresses, none, of course, is more important or interesting than the British Association Presidential Address of 1871, so well known to all. One of the earliest, on 'The Rate of a Clock or Chronometer as Influenced by the Mode of Suspension,' is most entertaining and suggestive as an example of the many side-lights' of a remarkable intellectual activity. Of great historical value is the Royal Institution lecture of 1856 on the 'Origin and Transformation of Motive Power'—already republished in Volume II. of the 'Mathematical and Physical Papers;' and one of the most interesting is that of late date (1892) on the 'Dissipation of Energy. In this much attention is given to the principle of Carnot, and here also occurs a remarkable statement which the author himself has thought worth while to print in italics;-it is :-"The fortuitous concourse of atoms is the sole foundation in Philosophy on which can be founded the doctrine that it is impossible to derive mechanical effect from heat otherwise than by taking heat from a body at a higher temperature, converting at most a definite proportion of it into mechanical effect, and giving out the whole residue to matter at a lower temperature."

The address on the opening of the Bangor Laboratories will be of interest to all who have to do with their like; that on the occasion of the unveiling of Joule's statue will interest everybody who cares for or who knows of the greatest generalization of modern science. In short, every page of this volume is deserving of the careful perusal of all who are devoted to Natural Philosophy in its most comprehensive sense, and who wish to know something of the spirit of one whose splendid contributions to physical science are, as a whole, greater than those of any other philosopher of the present time.

The mechanical execution of the book does not seem to be quite in keeping with the classical character of its contents, and its pages are occasionally marred by negligent proof reading. T. C. MENDENHALL.

WORCESTER POLYTECHNIC INSTITUTE.

The temperature data computed and plotted on maps as isotherms are not available in locating the boundaries of the zones, because they show the temperature of arbitrary periods-periods that have reference to a particular time of year rather than a particular degree or quantity of heat.

It is assumed that the distribution of animals and plants is governed by the temperature of the season of growth and reproductive activity-not by that of the entire year. The difficulty is to measure the temperature concerned.

Physiological botanists have long maintained that "the various events in the life of plants, as leafing, flowering and maturing of fruit, take place when the plant has been exposed to a definite quantity of heat, which quantity is the sum total of the daily temperatures above a minimum assumed to be necessary for functional activity." The minimum used by early botanists was

In the December issue of the National Geographic Magazine, Dr. C. Hart Merriam announces the discovery of the laws of temperature control of the geographic distribution of terrestrial animals and plants. Dr. Merriam has been engaged on this problem for sixteen years and believes he has at last obtained a formula which fulfills the requirements. He states that in the Northern Hemisphere animals and plants are distributed in circumpolar belts, the boundaries of which follow lines of equal temperature rather than parallels of latitude. Between the pole and the equator there are three primary belts or regionsBoreal, Austral and Tropical. In the United States the Boreal and Austral have each been split into three secondary transcontinental zones, of which the Boreal are known as the Arctic, Hudsonian and Canadian; and the Austral as the Transition, Upper Austral and Lower Austral.

cent writers believe that 6° C or 42.8° F more correctly expresses the temperature of the awakening of plant life in spring. "The substance of the theory is that the same stage of vegetation is attained in any year when the sum of the mean daily temperatures reaches the same value, which value or total is essentially the same for the same plant in all localities. This implies that the period necessary for the accomplishment of a definite physiological act, blossoming, for instance, may be short or long, according to local climatic peculiarities, but the total quantity of heat must be the same. The total amount of heat necessary to advance a plant to a given stage came to be known as the physiological constant of that stage." But students of geographic distribution are not concerned with the physiological constant of any stage or period in the life of an organism, but with the physiological constant of the species itself-if such a term may be used. "If it is true that the same stage of vegetation is

attained in different years when the sum of the mean daily temperatures reaches the same value, it is obvious that the physiological constant of a species must be the total quantity of heat or sum of positive temperatures required by that species to complete its cycle of development and reproduction." Now, "if the computation can be transferred from the species to the zone it inhabits-if a zone constant can be substituted for a species constant-the problem will be well nigh solved." This Dr. Merriam has attempted to do. "In conformity with the usage of botanists, a minimum temperature of 6°C (43°F) has been assumed as marking the inception of the period of physiological activity in plants and of reproductive activity in animals. The effective temperatures or degrees of normal mean daily heat in excess of this minimum have been added together for each station, beginning when the normal mean daily temperature rises higher than 6°C in spring and continuing until it falls to the same point at the end of the season." The sums thus obtained were plotted on a large scale map of the United States, and isotherms were run which were found to conform to the northern boundaries of the several zones. This is shown by colored maps. The data seem to justify the statement that "animals and plants are restricted in northward distribution by the total quantity of heat during the season of growth and reproductive activity."

In the case of the southern boundaries of the zones, it was assumed that animals and plants in ranging southward would encounter, sooner or later, a degree of mean summer heat they are unable to endure. "The difficulty is in ascertaining the length of the period whose mean temperature acts as a barrier. It must be short enough to be included within the hottest part of the summer in high northern latitudes, and would naturally increase in length from the north southward. For experimental pur

poses, and without attempting unnecessary refinement, the mean normal temperature of the six hottest consecutive weeks of summer was arbitrarily chosen and plotted on a large contour map of the United States, as in the case of the total quantity of heat."

On comparing this map with the zone map, the isotherms of 18°, 22° and 26°C were found to conform respectively to the southern boundaries of the Boreal, Transition and Upper Austral zones, leading to the belief that "animals and plants are restricted in southward distribution by the mean temperature of a brief period covering the hottest part of the year."

Except in a few localities the northern boundary of Austral species coincides with the southern boundary of Boreal species, but for a distance of more than a thousand miles along the Pacific coast a curious overlapping and intermingling of northern and southern types occurs. On looking at the temperature maps this is at once explained, for the mean temperature of the six hottest consecutive weeks from about lat. 35° northward to Puget Sound is truly Boreal, being as low as the mean of the corresponding period in northern Maine and other points well within the Boreal zone. On the other hand, the total quantity of heat is found to be the same as that required by Austral species. "It is evident, therefore, that the principal climatic factors that permit Boreal and Austral types to live together along the Pacific coast are a low summer tempera ture combined with a high sum total of heat."

A table is given showing the actual governing temperatures, so far as known, of the northern and southern boundaries of the several zones.

In conclusion, Dr. Merriam calls attention to the subordinate value of humidity as compared with temperature. "Humidity and other secondary causes determine the

presence or absence of particular species in particular localities within their appropriate zones, but temperature predetermines the possibilities of distribution; it fixes the

limits beyond which species cannot pass; it

defines broad transcontinental belts within which certain forms may thrive if other conditions permit, but outside of which they cannot exist, be the other conditions never so favorable."

Grasses of Tennessee-Part II.-F. LAMSONSCRIBNER.-University of Tennessee, Agric. Exper. Sta. Bull., VII. 1-141, 187 figures. 1894.

The first part of this important work treating of the structure of grasses in general, issued two years ago, is now supplemented by the part here noticed, containing descriptions and figures of all species known by the author to inhabit Tennessee. Carefully prepared keys to the genera and species are a feature of the book. The cuts are good, although printed on paper hardly firm enough to bring them out to the best advantage. The descriptions are diagnostic and couched in strictly technical language; on this point it is remarked: "Attempts to avoid tech

nical or 'hard' words often result in obscur

ing the meaning of the author, and an undue simplicity of expression is often apt to be offensive by implying a lack of intelligence on the part of the reader." As the book is intended primarily for the farmers of the State, this may be considered by some as a position of doubtful value.

It is to be regretted that the rules of nomenclature adopted by the botanists of the American Association for the Advancement of Science, which are practically those approved by the zoologists, have not been strictly followed. This will seriously hamper the usefulness of the book, for some of the names used by Prof. Scribner have become obsolete.

N. L. B.

THE University of Berlin is seriously crippled by the deaths of Helmholtz and Kundt. Their places cannot be filled, but Prof. Kohlrausch will probably be called to one of the vacant chairs.

THE Physical Review has published excellent portraits of Helmholtz, Kundt and Hertz, with biographical sketches by the editor-in-chief, Professor Nichols. Proba

bly the best account so far published in English of the work of Helmholtz is that contributed to the Psychological Review for January by Professor Stumpf, of the University of Berlin.

MR. F. Y. Powell, of Christ's College, succeeds Froude in the Regius Professorship of Modern History at Oxford.

ZOOLOGY.

A PICTURE-PUZZLE of a remarkable kind appears in the Zoologist for December. It is a reproduction of two photographs of a Little Bittern, showing the strange attitude assumed by the bird to favor its concealment. One of the figures shows the the bird standing in a reed-bed, erect, with neck stretched out and beak pointing upwards; and in this position it is difficult to distinguish the bird at all from the