TRANSACTIONS OP THE SECTIONS. 3^ 



included, according to the conclusions of Poisson, or the experiments of Wertheim, 

 which are at variance with each other. But these last changes are so small in the 

 bodies I am contemplating, that they may be neglected for all practical purposes. 

 Thus, from my experiments, the utmost extension of a bar of cast iron, 50 feet long, 

 is about 1 inch, or ^^dth of the length, and therefore the change of lateral dimen- 

 sions of the bar being only a fraction of this eotjdth, according either to Poisson 

 or Wertheim, it is too small to need including. The experiments from which I 

 deduced the utmost extension of cast iron, are given in the ' Report of the Com- 

 missioners on the Strength of Iron for Railway Purposes.' If the body strained 

 were wrought iron, brass, or others of a very ductile nature, the change of lateral 

 dimensions might, in extreme cases, be included. I beg to mention, with great 

 deference, that the profound work of Lame, lately published, ' On the Mathematical 

 Theory of Elasticity,' in which the elasticity is considered as perfect only, does not 

 appear to apply to such bodies as I have here treated of. 



Trigonometrical Survey. 



Communicaiion from Lieutenant- General Sir John Burgoyne, G.C.B., 



Inspector- General of Fortifications, regarding the progress made in the 



Publication of the Trigonometrical Survey. 



O. M. 0., Southampton, September 5, 1853. 



The labours of the Ordnance Survey Department have been directed during the 

 past year to the determination, according to the theory of minimum squares, of the 

 most probable corrections to be applied to the angles of the principal triangles. 



This process, which is a most laborious one, involving the solution of about 1300 

 equations of condition, is now well advanced, and every exertion is being made to 

 hasten its completion. Until it has been finally completed the computations of 

 distances cannot be properly undertaken, for it must be borne in mind that the trigo- 

 nometrical operations of the Ordnance Survey embrace a connected triangulation, ex- 

 tending through the length and breadth of the United Kingdom, which must be con- 

 sidered as a whole, in deducing the results. 



Besides preparing for the publicatiou of the principal triangulation, the Ordnance 

 Survey Department are about to publish a volume of Levels in Ireland, and another 

 of the Meteorological Observations made at the Ordnance Survey Office near Dublin, 

 the printing of both works being at the present time in progress. 



L. A. Hall, Lieut. -Colonel Royal Engineers. 



CHEMISTRY. 



On a Simple Instrument for graduating Glass Tubes. 

 By Thomas Andrews, M.D., F.R.S., M.B.LA. 



This instrument is intended to supply the chemist with a means of accurately gra- 

 duating his glass measures of capacity. The divisions admit of being varied in length 

 to the j7;ooodth of an inch, so as to allow the graduation to be adapted to the changes 

 In calibre of the vessel. They are obtained by the action of a micrometer-screw, 

 1 inch long, on a wooden block on which a standard scale is firmly fixed ; but the 

 details of the construction could not be rendered intelligible without a figure. Scales 

 exceeding 3 feet in length may be divided by means of this instrument, which the 

 author has very successfully employed in the construction of thermometers for delicate 

 investigations. The dividing instrument itself, and a thermometer graduated by its 

 aid, were exhibited to the Section. 



Exhibition of British Lichens, containing Dyeing Lichens. 

 By Professor Balfour, M.D., F.R.S.E. 



They were collected and prepared by Dr. Lindsay, and consisted of specimens of 

 Roccella tinctoria, R. fuciformis, Lecanora tartarea, Scyphophorus pi/xidatus, and Cla- 



