280 Sir J. W. Lubbock on a Graphical Method of 



vestigation in the study of a multitude of phsenomena in mole- 

 cular chemistry ; the results to be anticipated from which may 

 be as important as those which M. Biot has deduced from the 

 study of rotatory polarization. This method, besides, will pos- 

 sess the advantage of a more extended application. 



In regard to these subjects, I have only been able to make a 

 series of observations upon the sulphates mentioned above. 

 Notwithstanding the lively interest which I attach to re- 

 searches of this nature, I have been compelled to abandon them 

 for the present, as they would have led me too far from the 

 principal object towards which my efforts must be directed. 

 [To be continued.] 



XXXVI. Note on a Graphical Method of clearing a Lunar 

 Distance. By Sir J. W. Lubbock, Bart., F.R.S. ^c* 



BY the principles of the Gnomonic projection, to delineate an 

 arc of any given number of degrees beginning from any 

 given point S and in any given direction SR, the following 

 construction obtains. 



Let CPV be drawn per- 

 pendicular to the line PR 

 through C the centre of the 

 picture, and make VP in CP 

 produced = V~WT~CW, 

 D = CB being the distance of 

 the picture. D is"a constant 

 quantity, and is to be taken 

 of any convenient length. At 

 V make RVS equal to the 

 given angle. RS is the re- 

 quired delineation. 



In order to find graphically 

 the angles A B Cof a spherical 

 triangle, of which the sides 

 a, b, c are given, we have — 



1st. To delineate the triangle correctly by the rules of per- 

 spective. 



2nd. To ascertain the values of the original angles by means 

 of their delineations in the picture. 



Suppose, for example, we have the apparent zenith distances 

 or altitudes of two stars Sj, Sg, and their apparent angular 

 distance ; if we place Z the zenith at C the centre of the picture, 

 the following construction obtains for the accurate delineation of 

 the spherical triangle SjCSg : — 



* Communicated by the Author. 



