Royal Institution of Great Britain. 69 



tion of Colonel Colby ; and also of the measurement of a base in the 

 North of Ireland, upwards often miles in length. This base has been 

 measured by a set of beautiful compensation bars, devised by Col. 

 Colby, and executed in the most perfect manner by Mr. Troughton. 

 Two metals are used in their construction, which support cross bars 

 at their extremities, upon which dots are marked that never change 

 in their distance from each other, whatever change of temperature the 

 apparatus itself undergoes. These dots are observed by microscopes 

 themselves supported on compensation systems. The beauty and 

 perfection of the apparatus, the minuteness of work, and the accuracy 

 of performance, were illustrated by two bars, out of a set of six, which 

 are in course of construction by Messrs. Troughton and Sims, under 

 the orders of the East India Company, and are to be placed in the 

 hands of Capt. Everest for the purpose of an exact survey in the 

 East. Mr. Faraday drew his instruction this evening from Capt. 

 Drummond and Lieut. Portlock, two officers who have been exten- 

 sively engaged in the Irish measurement. 



May 14. — Mr. Burnett on the operation of lithotrity, with the 

 history of the discoveries of Le Roy, Civiale, Heurteloupe, &c. &c. 

 Baron Heurteloupe's apparatus was upon the table, and also that of 

 M. Civiale ; and the general principles of the operation were shown, in 

 various ways, upon different calculi. Several cases were adduced to 

 show the value of this great discovery in modern surgical practice. 



May 21 . — Mr. Faraday on the application of a new principle in the 

 construction of musical instruments. The principle here referred 

 to is that which has lately been so popular in the small musical in- 

 struments called iEolinas. A spring generally in the form of a pa- 

 rallelogram being fastened at one end to a plate with an aperture 

 of corresponding size, so as nearly to fill the latter, is put into iso- 

 chronous vibration when the breath is urged past it, and produces mu- 

 sical sound. The laws of the vibrations of rods and springs were re- 

 ferred to, and then all the instruments which have been constructed on 

 this principle, from the ancient Chinese organ to Mr. Day's iEolian 

 organ, were produced and explained : amongst them were of course 

 the iEolina and Mr. Wheatstone's orchestrion, the fingering and 

 powers of which were fully explained. Each instrument had its ca- 

 pabilities exhibited by performances. Mr. Wheatstone supplied the 

 philosophy of the evening. 



May 28. — Capt. Manby on the means of preserving lives in cases 

 of shipwreck, and on a new practical mode of hauling life-boats, &c. 

 through the surf. Capt. Manby gave an account of his own apparatus 

 for these important purposes, and illustrated it by experiments and 

 drawings. That part which related to the preservation of shipwrecked 

 mariners is already before the public ; but his method of hauling a boat 

 off from shore is new, and is said to have been found useful. An an- 

 chor with a buoy to it is laid out at any previous time beyond the line 

 of surf, a block is fastened to the buoy so that it cannot turn, a rope is 

 passed through this block and both ends brought onshore; but to 

 prevent the rope sinking into the sand, a small buoy is made fast 



to 



