yune 2, 1887] 



NATURE 



99 



Next comes a curious suggestion of analogy between 

 the behaviour of fluorescent bodies (which always degrade 

 the refrangibHity of the light they give off) and the heat- 

 radiation from bodies which have been exposed to sun- 

 light. Sunlight, as it reaches us after passing through 

 the atmosphere, is less rich in ultra-red rays than is the 

 radiation from the majority of terrestrial sources ; while 

 the radiation from bodies which have been heated by 

 direct sunlight is entirely ultra-red. Here we have, for the 

 terrestrial atmosphere, the "green-house theory" which, 

 in the second course, was applied to explain some of the 

 singular phenomena exhibited by comets. 



This is followed by an extremely interesting discus- 

 sion of the functions of the colouring- matters of blood 

 and of green leaves :— with the contrasted effects, 

 upon plants, of total deprivation of light, and of con- 

 tinuously maintained illumination. A particularly valu- 

 able speculation, as to the probable nature of the behaviour 

 of chlorophyll, is unfortunately too long for extraction. 



So far, radiation has been treated without any special 

 reference to vision. But the author proceeds to describe 

 the physical functions and adaptations of the eye :— with 

 particular reference to the arrangements for obviating 

 such of the theoretical defects as, while involved in its 

 general plan, ivoiild also tetid to dhnitnsh its practical 

 usefulness. The introduction of this obviously natural 

 proviso, one which we do not recollect having seen pro- 

 minently put forward till now, exhibits in a quite new light 

 the intrinsic value of those objections to the " argument 

 from design" which have been based upon the alleged 

 ^imperfection of the eye as an optical instrument. 



The analogy of fluorescence is once more introduced, 

 but now for the purpose of suggesting a mechanical ex- 

 planation of the mode in which the sense of vision is 

 produced. This is brought forward after the modern 

 photo-chemical theory of vision has been discussed. The 

 latter is not altogether dismissed as improbable, but some 

 of the more important difficulties which it raises are 

 pointed out. The triplicity of the colour-sense, and the 

 mechanism of single vision with two eyes, are treated at 

 some length. But throughout this part of the work it is 

 frankly confessed that there are many elementary ques- 

 tions, some of fundamental importance, which we are 

 still unable even approximately to answer. 



In his final chapter, the lecturer, in conformity with 

 the terms of his appointment, discusses the argument 

 from design. The origin of life, and the origin of species 

 are boldly (though all too briefly) treated : — next comes 

 the question of the adaptation of physical structure, 

 specially of course that of the eye, to the modes of life 

 and the wants of animals. 



" There is some very intimate connection between 

 thinking, as we know it in ourselves, and the condition of 

 the brain. .So close is the connection that some have 

 supposed that thinking is a mere function of the material 

 organism, conditioned by nothing more than the motions 

 of the molecules of which that organism consists. But 

 surely this is going far beyond a legitimate inference from 

 the observed facts. The body of a living animal is obe- 

 dient to the laws of motion, the law of gravitation, and 

 similar laws of the kind which belong to dead matter. 

 But that does not prove that life is nothing more than a 

 ■process depending on such laws. So if thinking be 

 accompanied, as wc know it in ourselves to be accom- 



panied, by a state of activity of the material organism of 

 which the body consists, that does not prove that think- 

 ing is nothing more than an action of the material 

 organism. We have seen that life can only proceed 

 from the living ; may it not be in a similar manner that 

 mind can only proceed from that which has mind ? See 

 what the contrary supposition leads us to. Here is man, 

 in a geological sense a creature but of yesterday, utterly 

 incapable of accounting for his own existence by any 

 play of mere natural forces, and yet ignoring the existence 

 of any mind higher than his own mind, though ready 

 enough to admit the existence of unintelligent law, and 

 that without lim'tations of time or space." 



No higher praise need be bestowed on the scientific 

 part of this third volume than is involved in saying that 

 it is a worthy successor to the other two. Together, they 

 form a singularly instructive, and yet (in the best sense) 

 popular, treatise on a fascinating branch of natural philo- 

 sophy. Were this their only aim, no one could deny 

 that it has been thoroughly attained. 



But their aim is of a loftier character. Here and there 

 throughout the work there have been occasional refer- 

 ences to the main purpose which has determined the 

 author's mode of arranging his facts and his deductions 

 from them. In the few closing pages this purpose is 

 fully developed, and a brief but exceedingly clear state- 

 ment shows at once how much in one sense, and yet how 

 little in another, can be gathered as to the personality 

 and the character of the Creator from a close and reverent 

 study of His works. 



These closing pages point out distinctly the danger 

 alike of totally neglecting, and of too exclusively study- 

 ing, the grandeur of nature. The first holder of this new 

 post has set a noble example to his successors. He has 

 supplied, not only to them but also, and we hope espe- 

 cially, to the rapidly-changing quaternion of neo-teleo- 

 logists who will soon be set at work in the Scottish 

 Universities, a warning which they will do well to lay to 

 heart : — 



" If we confine our attention to the study of nature in 

 all its immensity, our conceptions of its Author are in 

 danger of merging in a sort of pantheistic abstraction, 

 in which the idea of personality is lost." 



P. G. Tait. 



OUR BOOK SHELF. 



Our Bird Allies. By Theodore Wood. (London : 

 Society for Promoting Christian Knowledge, 1887.) 



The author of this little book holds that no British bird 

 is utterly and wholly destructive, but that the misdeeds of 

 even the most mischievous are atoned for in some degree 

 by services rendered to us in other ways. Birds aid us, 

 he points out, in three ways — first, by acting as sca- 

 vengers, and destroying putrid matter ; secondly, by 

 devouring the seeds of the various wild plants which are 

 so troublesome upon cultivated land ; thirdly, and most 

 important, by the slaughter of insects. The limitations 

 of space have prevented Mr. Wood from mentioning all 

 the birds he would have liked to describe, but he has 

 found room for an account of most of the British birds 

 which are especially beneficial. He writes simply, clearly, 

 and with adequate knowledge ; and there are probably 

 few farmers who would not profit by studying what he 

 has to say on a subject in which they ought to be strongly 

 interested. He expresses his firm conviction that 

 agriculture, as a profitable undertaking, is absolutely 



