Jnuc 1 1, 1874J 



NA TURE 



105 



are immediate and evident ; it is believed that special cases of 

 pi'oportionality are involvei in the general relation, and hence 

 that Newton's Second Law is an a priori cognition. 



rUit the cognition which his opponents aftirm is a very diffe- 

 rent cognition, though this is an odd name to give to a mathe- 

 matical doctrine. What his opponents affirm is that in certain 

 cases forces measured in a certain way are proportional to their 

 effects measured in a certain way ; and by proportional they 

 mean proportional and not something else. They aflirm that 

 experiment and observation are necessary to ascertain tliis pro- 

 portionality ; and that experiment and observation, and the 

 method of verification, furnish overwhelming evidence in favour 

 of the truth ot Newton's laws. Their best proof is the Naiiti- 

 ral Almanac, to those who can understand it and them. 



I believe the « priori method to be as utterly barren in the 

 future as it has been in the past. Wlien a new truth has been 

 discovered it is easy to say that it is evident ii priori. Some day 

 the laws of the actions of molecules and their relations to heat 

 and electricity will be discovered by physicists ; but I imagine 

 they will be physicists of the type of Rumford and Faraday and 

 Thomson and Slaxwell. Meantime it is open to any aprioii 

 philosopher to anticipate the future. 



And now, as far as I am concerned, this correspondence will 

 cease. Mr. Collier is polite enough to say that ray letter would 

 have confirmed Sir W. Hamilton in his conviction that the 

 narrow discipline of mathematics produces an incapacity for 

 general reasoning ; and he therefore cannot be anxious to con- 

 tinue a correspondence with one so contemptible, so stupid, and 

 so ignorant as he plainly believes me to be. 



A Senior. Wrangler 



I SH.iil.L be obliged if you will permit me to correct a verbal 

 error, of some importance, in my letter (Nature, vol. x. p. 84). 

 The words " fiiiis/icd conception,'' in col. 2, line 26, should be 

 "Jinis/ici/ preconception." J. Coi.i.TER 



The Glacial Period 



Both Mr. Belt and Mr. Bonney, have, I think, missed the 

 one point on which the question under discussion turns. The 

 shell-bearing drift-gravels are well stratified. T can speak to those 

 in the neighbourhood of Macclesfield, which nm up to 1, 100 ft. 

 above the sea, being also very delicately current-laminated. I 

 am puzzled to imagine how this structure could be obtained if 

 the gravels were brought to their present position in the way Mr. 

 Belt supposes ; indeed its presence seems to me fat.al to his 

 hypothesis. It is not the case moreover that all the shel's are 

 smashed and scratched. At Macclesfield most of the shells are 

 broken, as one would expect to be the cise if they had been 

 tossed .about on a shingle-beach ; but entire specimens were not 

 very rare. As for scratches, I never saw one on either the shells 

 or the pebbles of these gravels ; in the boulder clay, where the 

 included stones are scratched, scratches are occasionally seen on 

 the shells as well. A. H. Green 



Cockermouth, June 6 



VENUS'S FLY-TRAP {Dioncea miiscipula)* 



THERE are two ways of studying a plant or an animal. 

 One of these consists in the mere contemplation and 

 description of its external aspects and behaviour. Persons 

 who occupy them^eIves with this sort of study are com- 

 monly called naturalists ; for it is by them that by far 

 the greater proportion of the facts we possess relating to 

 natural objects has been gained. 



But there is another and a much better sense in which 

 a man may be said to be a naturalist. The true natu- 

 ralist does not content himself with standing at one side 

 and watching the proceedings of nature as a mere spec- 

 tator. Animated by that insatiable scientific curiosity 

 from which some shrink, in ttie fear lest it shoulrl carry 

 them too far, while the greater part are indifferent, 

 he occupies his whole life in seeking to lift the veil 

 Irom all that is hidden in nature and in discovering 

 and exposing the springs of every secret process. 

 His restless spirit cannot content itself with contem- 

 plation of the mere external aspects of living beings nor 

 even with the most minute and se.^.rching study of the 

 forms and structure of organic life. For even if he begin 



* Leclue by Dr Burdon Sanderson, F.R.S., at the Royal Institution, I'ri- 



as a botanist or zoographist, a mere describer of plants 

 or animals, he is forced by the perception of that general 

 adaptation of means to ends and ends to means which he 

 sees everywhere, to become first an anatomist then a 

 physiologist. The study of these external aspects leads 

 him, if possessed of that curiosity which is his charac- 

 teristic attribute, to study their minute structure, and 

 this, the further he goes into it, stirs up in him the 

 desire to penetrate further into the mysteries of their 

 being. For the delight and interest with which the forms, 

 colours, and structure of animals and plants fill us is de- 

 rived from the conscious or unconscious perception by 

 our minds of their adaptation— i\\e\i- fitness for the place 

 they are intended to occupy. I would go further even than 

 this, and maintain that our artistic perception of beauty in 

 nature is, I believe, in great measure derived from the 

 same source. 



But to understand nature in the sense of the naturalist 

 we must know not only those aspects which she is wilhng 

 to present to us but those she is determined to hide. For 

 this end, when we cannot get at what we want by per- 

 suasion, we are often obliged to use compulsion. 



It is constantly happening to the naturalist, that he has 

 a process, a contrivance before him, a series of pheno- 

 mena the connection or evolution of which he cannot 

 understand. He stands at one side and watches and 

 learns but little, for nature refuses to tell :u/'iy she does this, 

 or /hkli that. Under these circumstances, which recur, not 

 once in a way, but daily and hourly in the study of plant 

 and animal life, what is he to do ? Is it his duty to sit 

 down respectfully and wait, in the hope that what is now 

 difficult and obscure may, by the light thrown upon it 

 from right or left, become more or less clear and intelli- 

 gible .' No. This is not the spirit of the naturalist. If 

 nature conceals the truth, we frankly deny her right to 

 do so, and wrest it from her by force. If circumstances 

 are unfavourable, we alter them to suit our ends. If, as 

 repeatedly happens, a number of antecedents are seen to 

 lead to one event, if a number of apparent causes conspire 

 to one result, we proceed in our investigation by taking 

 away first one, then others of these antecedents, until by 

 a succession of trials (or as they are commonly called 

 experiments) we find the true one, viz. that of which the 

 removal or modification abolishes or alters the event. It 

 is thus, and thus alone, that we compel nature to tell 

 '■ that wherein her great strength lies." 



It is my purpose in this lecture to illustrate to you if I 

 can, by an example, that the systematic application of 

 the method ot experiment is the only method by 

 which it is possible to become so acquainted with the 

 forces of nature as eventually to be able to convert them to 

 useful purposes (and this is one, though by no means the 

 highest, end of natural knowledge). More particularly is 

 it true of that branch of natural knowledge which par cx- 

 cclh'iicc we call physiology, that it is by experiment alone 

 that progress has been or can be made ; the whole 

 subject being in its present state but a system of czp;ri- 

 inental results. 



A while ago I applied the term forcible to this method 

 because it is the plan by which, as Bacon said, we torture 

 nature. But let us remember that this is a inere figure 

 of speech. In disciplining nature to our ends, in forcing 

 her to give up her secrets, we use no violence, but utmost 

 gentleness. Plant or animal, to be made to tell its story, 

 must be delicately handled, so delicately that, by asso- 

 ciation, the very care which the naturalist, for scientific 

 ends, bestows on animals and plants, unavoidably en- 

 genders a love for them. However right and nec-ssary it 

 may be that we should to-night destroy and m mgle these 

 beautiful leaves for our own pleasure and instruction, let 

 us not do so recklessly, for the life and beauty we destroy 

 we cannot with all our science bring back .again or imitate. 



The name Dionrca imiscipi/hi was given to the plant 

 when it was first imported from America. It belongs to 

 the family I )roseracr;E, a very natural one, i.e. one in 



