396 Retrospective Criticism,' 



name is too humble to add any weight to the recommendations of K. or to' 

 my own ; but should any thing of the kind be seriously undertaken, the 

 little time and talent I have, if acceptable, will be cheerfully devoted to its 

 promotion. — J. R. St. John Street Road, July 3. 1829. 



Chinese Ornithological Literature. — In the public library at Petersburgh 

 there is a Chinese work on ornithology, most beautifully drawn and painted. 

 {Jones's Travels.) Now the Chinese are well known to excel in drawing 

 and painting subjects of natural history, and it would be well worthy of the 

 greatest exertions to endeavour to obtain permission to copy this work. — 

 Rmticus in Urbe. 



Art. X. Retrospective Criticism, 



Ascent of the Aerial Spider. — Sir, Your Magazine for July last (p. 299.), I 

 perceive, contains a second letter from Mr. Murray on the "ascent of the 

 aerial spider." Altthough I have distinctly announced that the principle 

 upon which I explain the ascent of the spiders which produce gossamer has 

 long been familiar to men of science ; that I make no pretensions whatever 

 to the discovery of any new principle ; but that my claim to originality is 

 founded solely on the application of one already known, to the solution of 

 this interesting problem in natural history; still Mr. Murray reiterates his 

 charge of want of novelty j remarking, that I apply the principle to the 

 ascent of the spiders, exactly as M. Gay Lussac applied it to the soap bubble. 

 The question to be decided is, whether the application which I have made of 

 this principle had been made previously by M. Gay Lussac, or any other 

 individual. I believe that it had not. My claim to originality, therefore, 

 holds good, and I am not at all induced to forego it. Let Mr. Murray submit 

 his electrical hypothesis to the same test, and see what will become of its 

 novelty. His principle is not new ; and the fact, that excited bodies, in dif- 

 ferent electrical states, mutually attract each other, is not new. What then 

 is left for Mr. Murray, but the application of the principle to the ascent of 

 the spider? but, according to his mode of reasoning, he cannot avail himself 

 of this circumstance. Controvertists should be careful not to entangle 

 themselves in the snares which they spread for their antagonists. 



In alluding to my comments on the experiment made with tiie spider in his 

 library, Mr. Murray proceeds thus : — " Because I did not mention the tem- 

 perature within and without, ergo I had not taken it, and had not ascertained 

 the direction of the current. Now, Mr. Blackwall may have, if he presses 

 for it, all the benefit that may arise from his illogical conclusion." What ! 

 does Mr. Murray, who has evinced so much anxiety to impress his readers 

 with the idea, that h6 has " not ventured beyond the pale of sound and sober 

 reasoning in the true spirit of inductive science," unhesitatingly admit, that, 

 in giving publicity to this experiment through the medium of the press, he 

 has designedly withheld particulars calculated to exercise an important in- 

 fluence on the result ? Perhaps Mr. Murray is desirous that a tacit assent 

 should be given to the conclusion at which he has arrived, independently of 

 any examination of the premises from which it is deduced. If so, I can easily 

 conceive, that he may have weighty reasons for giving an imperfect detail of 

 circumstances calculated only to mislead. In what manner the promulga- 

 tion of partial evidence, and the intentional withholding of facts essential to 

 a correct estimate of his experiment, are to promote the cause of truth, the 

 principal object which Mr. Murray professes to have in view, I leave for him 

 to determine; and, if I mistake not, it will require all his skill in logic to 

 extricate him from the dilemma in which he has so rashly involved himself. 



The doctrine of the composition of forces, which I have introduced to 

 explain the various oblique directions in which spiders are conveyed through 



