32 



KNOWLEDGE 



[December 2, 1889. 



the bands that pass regularly across the spectrum of a 

 rising or settinj,' star must be very distant from the observer, 

 or they would not in general be affected by the earth's 

 rotation rather than by the winds blowing. We are there- 

 fore di-iven to the conclusion that the difference of the 

 temperature, between the masses of air causing the imequal 

 refraction and the sm-rounding air, must be small compared 

 ■with the himdredth part of a degree Fahrenheit. 



Xottcts of Boofes. 



Dixedsex of Plants. By H. JIaeshall Ward, M.A., 

 F.R.S. (Christian Knowledge Society.) We cannot 

 conceive of a better introductory text-book on the subject 

 of plant diseases caused by micro-fimgi than this new 

 volume of the " Romance of Science Series," nor could 

 the subject have fallen into the hands of anyone better fitted 

 than Prof. Marshall Ward to jiopularise it without in the 

 sUghtest degree deviating from scientific accuracy. There 

 is a freshness of style, a terseness and felicity of expression, 

 and a lucidity of exposition that is quite fascinating, and 

 that entices the reader on through chapter after chapter, 

 as he follows the author in his description of the romantic 

 adventures of first one kind of fungus spore and then 

 another. A book which detaOs with minute acciu-acy the 

 life history of such scom-ges as the " potato disease," 

 caused by P/ii/topIithoni infcstnns, the " hop-mildew," and 

 the "smut," "rust," and "ergot" of cereals, cannot 

 faU to be of interest and value to aU practical men. If to 

 be fore-warned is to be fore-armed, and if to know one's 

 enemy is the best possible preparation for taking measures 

 to protect oneself against him, then this book ought to be 

 in the hands of every practical horticulturist and agri- 

 culturist of any pretensions, and to be diligently studied 

 from end to end. The paper, t\'pography, and illustra- 

 tions are everything that could be desired. 



Toilers in the Sea. By M. C. Cooke, M.A., LL.D. 

 (Christian Knowledge Society.) This is something more 

 than a mere popular exposition of the wonders of marine 

 invertebrate Ufe, and many who have long been students 

 of the fauna of the sea will be gi'ateful to Dr. Cooke for 

 ha^■ing gathered into convenient compass so complete an 

 epitome of the results of modern research — results which 

 are scattered through such a wide series of scientific 

 journals that access to a good library and many hours of 

 patient search are often necessary for the verification of 

 facts. The scheme of the work has necessitated that only 

 those groups of invertebrates should be included which 

 possess solid parts capable of preservation in the dry con- 

 dition, and in the investigation of which the microscope 

 will be largely used ; hence Foraminifera, Polycystina, 

 Sponges, Sertularian Hydroids, Corals, Alcyonarians, 

 Polyzoa, and Tube-worms are the only groups discussed. 

 Notwithstanding Dr. Cooke's defence of the title he has 

 selected, we stOl think that, as very few of the structures 

 referred to are really marine " Homes without Hands," it 

 would have been better to have avoided an expression 

 which in almost every case suggests a wrong relation 

 between the object described and the animal of wliich it 

 formed a part. This, however, is a minor pomt, and 

 there is httle in the book itself but will tend to dissipate 

 the too commonly received notion that such structures as 

 coral, for example, are formed by the united efforts of 

 numbers of minute creatures which toiliiti/li/ raise, little 

 by little, structm-es which ultimately reach gigantic dimen- 

 sions. The book is deUghtfully written and well illustrated. 



and contains an enormous amount of information from the 

 best possible sources. To amateur microscopists especially 

 we would most cordially commend it, and we feel sure that 

 if they will only take it as the companion to then favourite 

 instrument, they wUl be able to form far more intelligent 

 ideas concerning the nature of many of the beautiful 

 objects which are popular in microscopical exhibitions, 

 than are at present, unfortimately, generally to be met 

 with. 



Wayside Sketclies. By F. E. Hulme, F.L.S. (Christian. 

 Knowledge Society.) This is a book of gossip, on an 

 endless variety of subjects connected with rural life and 

 the roimd of the seasons ; but it descends, we fear, too 

 frequently to the level of commonplace, and the chapters 

 are far too long. The iQustrations, nearly seventy in 

 number, are a redeeming. featm'e, being varied in subject, 

 and, as a rule, accurate and artistic in execution. 



GROWTH AND DECAY OF MIND. 



P>y THE LATE R. A. PrOCToR. 



{(.'iintinued from j). 'iril.) 



IT cannot be questioned that with old age there 

 comes a real physical incapacity for original 

 work, whQe the power of maturing past work 

 remains comparatively but httle impaired. Dr. 

 Carpenter has shown how this may partly be 

 explained by the physical changes which lead in old age 

 to the weakening of the memory ; or perhaps we should 

 rather say that in the follo\\ing passage liis remarks 

 respecting loss of memory serve to illustrate the loss of 

 brain power generally, and especially of the power of 

 forming new ideas, in old age. " The impahment of the 

 memory in old age," he says, " commonly shows itself in 

 regard to new impressions ; those of the earUer period of 

 life not only remaining in full distinctness, but even it 

 would seem increasing in Advidness, from the fact that the 

 eye is not distracted from attending to them by the con- 

 tinued influx of impressions produced by passing events. 

 The extraordinary persistence of early impressions, when 

 the mind seems almost to have ceased to register new 

 ones, is in remarkable accordance with a law of nutrition 

 I have formerly referred to. It is when the brain is 

 growing that the direction of its structure can be most 

 strongly and persistently " (query lastingly ?) " given to 

 I it. Thus the habits of thought come to be formed, and 

 j those nen-e-tracks laid down which (^as the physiologist 

 believes) constitute the mechanism of association, by the 

 time that the brain has reached its maturity ; and the 

 nutrition of the organ continues to keep up the same 

 I mechanism in accordance with the demands upon its 

 I activity, so long as it is being called into use. Fm-ther, 

 dm-ing the entire period of vigorous manhood, the brain, 

 like the muscles, may be taking on some additional growth, 

 I either as a whole or in special parts ; new tissue being 

 I developed and kept up by the nutritive process, in accord- 

 ' ance with the modes of action to which the organ is 

 I trained. And in this manner a store of ' impressions ' or 

 ' traces ' is accumulated, wliich may be brought within the 

 ' sphere of consciousness ' whenever the right suggesting- 

 strings are touched. But as the nutritive actirity 

 diminishes, the ' waste ' becomes more rapid than the 

 renovation ; and it would seem that while (to use a com- 

 mercial analogy) the ' old-established houses ' keep their 

 ground, those later firms, whose basis is less secm-e, are 

 the first to criunble away — the nutritive activity, which yet 

 suffices to maintain the original structure, not being 

 I capable of keeping the subsequent additions to it in 



