J()(j COUNT RUMFORD's NEW EXPERIMENTS 



Taking the capacity of bra is for heat (o be to that of water 

 as 0,11 to 1, it appears, that the capacity of the metallic box, 

 weighing 6850 grains, is equal to the capacity of 622 grains 

 of water; and adding this quantity of water to that contained 

 in the box, we fliall have the capacity of the refervoir pre- 

 pared for the experiments equal to that of 1932 grains of 

 water. 

 The tempera- Each refervoir is kept in its place by a cylinder of dry wood, 

 ter in each was" Qne °^ tne extremities of the cylinder being fixed in a focket 

 ihewn by a ther- in the center of the interior face of the refervoir ; and each 

 refervoir has a little neck, through which it is filled with water, 

 and which after receives the bulb of a cylindrical thermometer, 

 that reaches completely acrofs the infide of the box in the di- 

 rection of its diameter. 



The two refervoirs of heat, with their two lenfes, are firmly 

 fixed in an open frame, which, being moveable in all directions 

 by means of a pivot and a hinge, the apparatus is eafily di- 

 rected toward the fun, and made to follow its motion regularly, 

 fo as to keep the folar fpectra conftantly in the centers of the 

 blackened faces of the refervoirs. 

 Light admitted In order that the quantities of light palling through the two 

 through equal j en f es fl 10 uld be perfectly equal, a circular plate of well po- 

 lifhed brafs, in the centre of which is a circular hole three in- 

 ches and a half in diameter, is placed immediately before each 

 of the Ienfes. 



When the refervoirs of heat are placed at different diftances 

 from the focufes of their refpeclive lenfes, the diameters of the 

 folar fpectra, which are formed on the blackened faces of the 

 refervoirs, are neceffarily different; and as the quantities of 

 light are equal, its denfily at the furface of each refervoir is 

 inverfely as the fquare of the diameter of the fpedrum formed 

 on that furface. 



Experiment I. 



Experiment. In this experiment the refervoir A was placed fo near the 



With equal focus of the lens, between the lens and the focus, that the 



fdlar'i^ots from diameter of the folar fpedrum falling on it was only \ an inch, 



the lenfes were or 6 lines, while the refervoir B was advanced fo far before 



lines diam. ** ^ e ** ocus > lnat tne fpeftrum was two inches in diameter, or 



24 lines. 



As 



