224 Prof. Draper's Description of the Tithonometer. 



the yellow, insulated by the same, being marked 3 ; the inter- 

 vening region being divided into two equal spaces, and divisions 

 of the same value carried on to each end of the spectrum. 



As instruments will no doubt be hereafter invented for measur- 

 ing the phenomena of different classes of rays, it may prove con- 

 venient to designate the precise ray to which they apply. Per- 

 haps the most simple mode is to affix the name of the ray itself. 

 Under that nomenclature the instrument described in this paper 

 would take the name of Indigo-tithonometer. 



There is no difficulty in adapting this instrument to the deter- 

 mination of questions relating to absorption, reflection, and trans- 

 mission. Thus I found that a piece of colorless French plate- 

 glass transmitted 866 rays out of 1000. 



Description of the Instrument. First, of the glass part. — 

 The tithonometer consists of a glass tube bent into the form of 

 a siphon, in which chlorine and hydrogen can be evolved from 

 muriatic acid, containing chlorine in solution, by the agency of a 

 voltaic current. It is represented by fig. 1, where a b c is a clear 

 and thin tube four tenths of an inch external diameter, closed at 

 the end a. At d a circular piece of metal, an inch in diameter, 

 which may be called the stage, is fastened on the tube, the dis- 

 tance from d to a being 2-9 inches. At the point x, which is two 

 inches and a quarter from d, two platina wires, x and y, are fused 

 into the glass, and entering into the interior of the tube, are des- 

 tined to furnish the supply of chlorine and hydrogen ; from the 

 stage d to the point b, the inner bend of the tube, is 2-6 inches, 

 and from that point to the top of the siphon c, the distance is 

 three inches and a half. Through the glass at z, three quarters 

 of an inch from c, a third platina wire is passed ; this wire termi- 

 nates in the little mercury cup r, and x and y in the cups p and 

 q respectively. 



Things being thus arranged, the instrument is filled with its 

 fluid prepared, as will presently be described ; and as the legs a b, 

 b c, are not parallel to each other, but include an angle of a few 

 degrees, in the same way that Ure's eudiometer is arranged, there 

 is no difficulty in transferring the liquid to the sealed leg. Enough 

 is admitted to fill the sealed leg and the open one partially, leaving 

 an empty space to the top of the tube at c of two and three quar- 

 ter inches. 



