178 Proceedings of the Cambridge Philosophical Society. 



any required duration, as applicable to light-house purposes, invented by 

 Robert Aytoun, Esq. S. S. A,, was exhibited in operation, a description 

 of it read, and a committee appointed to examine and report. 



4. An instrument for enabling tailors to find the proper position of the 

 " sye" or sleeve of coats, and the proper hanging of the ** skirts," invent- 

 ed by Mr Jamks M'Donald, tailor, West Register Street, Edinburgh, 

 was exhibited, and a description of its nature and uses, illustrated by two 

 drawings, was read, and the drawings presented to the Society by Mr 

 M'DoNALD. A committee was appointed to examine into the merits of 

 the invention. 



David Boswell Reid, Esq. and John R. Skinner, Esq. W. S. were 

 elected Ordinary Members. 



3. Proceedings of the Cambridge Philosophical Society. 



March 31, 1829. — The Rev. Professor Gumming Vice-President, being 

 in the chair, 



A memoir was read by J. Challis, Esq. of Trinity College, on the vibra- 

 tions of an elastic fluid, in which the author maintained that the disconti- 

 nuous functions introduced into the investigations on this subject by La- 

 grange, were inconsistent with the analogies of mathematical reasoning, and 

 unnecessary for the solution of the problem. 



A paper by J. W. Lubbock, Esq. of Trinity College, was also read, on 

 the comparative probabilities of life, as obtained from the recorded observa- 

 tions of London, Northampton, Carlisle, Chester, France, Paris, Mont- 

 pellier, Holland, Amsterdam, Brussels, Breslaw ; and on various other 

 points in the calculation of such probablities, and of annuities depending 

 upon them. 



After the meeting. Professor Henslow gave an account, illustrated by a 

 collection of coloured drawings, of the organization and classification of ferns. 



May 4. — Dr Frederick Thackeray, the treasurer, being in the chair. 



Some observations were made by Professor Whewell, on the systems of 

 mineralogical classification, recently proposed by Nordenskiold, Bonsdorff, 

 Keferstein, and Naumann ; and the preference was given to the latter, as 

 the one which best answers the condition of establishing a correspondence 

 between the classes founded on chemical constitution and those connected 

 by physical resemblances. 



After the meeting the Rev. Leonard Jenyns gave a description, illustrated 

 by drawings, of the construction of feathers, their uses and the mode in 

 which these are provided for ; and the manner of their origin and growth. 



May 18. — Dr F. Thackeray, the treasurer, being in the chair, a paper 

 by W. H. Miller, Esq. of St John's college, was read; "on the caustics 

 produced by successive reflections at a spherical surface." 



A memoir was also read by the Rev. R. Willis, "on the mechanism 

 of the glottis," in which the author explained the conditions under which 

 sound is produced by air passing between the edges of two membranes, and 

 the manner in which the muscles of the larynx bring the organs into and 

 out of the positions which are thus required. This communication was 



