2r)f) 



sued in tlu> latter ; hut stiii it is remarkiihle that tlie most useful 

 speculations, in a theoretical point of view, should excite so little 

 attention. The author proposes to supply the deficiency here felt, 

 by examining in detail simple problems of wave motion, in every 

 possible form of canal or channel, and intends to apply t\\v. results 

 to the motion of the tide-wave, and similar problems. The results 

 which he has already laid before the Society, are merely the intro- 

 ductory steps, comprising the discussion of the general form of 

 uniform and perfect wave-motion, and an approximative solution 

 «if the problem of solitary translation. In other memoirs, he hopes 

 to apply similar processes to incipient motion, retarded motion, and 

 the combination of extraneous forces with internal cohesion. 



2. On a New Method of shewing the Unequal Expansion of 



Crystals. By Professor Forbes. 



This method is founded on the expedient devised by Mitscher- 

 lich, of obtaining two images of a minute distant object from a sec- 

 tion of a hemitrope crystal of selenite, which is flat when cold, but 

 is composed of two inclined surfaces when heated. By throwing 

 the sun's image, reflected from such a surface, on a distant wall, 

 the gr.idual formation of the double image during heating may be 

 seen by any number of persons. 



3. On the Diminution of Temperature with Height in the 



Atmosphere at different Seasons of the Year. By the 



same. 

 The results communicated to the Society were obtained from 

 nearly five years of simultaneous observations, made twice a-day 

 at Colinton and at the Bonally reservoir fve miles south-west from 

 Edinburgh. The height of the former station fibove the level of 

 tiie sea is 3G4 feet, of the latter 1100 foet exactly; the diffxirence 

 7^6 feet. The mean annual diff^orence of temperature amounted 

 to 3\22, giving 229 feet of ascent for a diminution of temperjiture 

 of 1' Fahr. The influence of the seasons is briefly shewn by the 

 following mmibers : 



Months, Jnn. Ffli. Mar Ajir. May Juno July Aui;. .Sept. Oct. Nov. Dec. 



'*ofTemT") -•'" '-^' •^•''^ ^"'^ '^■^'^ -^'^ ^-^^ ^-7* ^-^2 3.13 1.90 2.49 

 PeetfmP. 3r,l 310 204 159 ir,7 194 229 197 236 235 387 290 



That the decrement of temperature is most rapid in summer, 

 and least so in winter, has been long known. Its highest value 



