tfluence of 



319 



t 



1* 



tliat, as in his experiments the temperature of the air which sup- 



flied oxygen for combustion in the sunshine, was about 12"^ 

 ah, above that in the darkened room, the rarefaction produced 

 by heat might exercise some influence in retarding the rate of 



burning in the sunhght 



In conducting my experiments, I endeavored to secure two 

 conditions^ viz: 



1. Absolute calmness in the atmosphere. 



2. Exposure of the flame to the influence of intense solar 



light, without heating the surrounding air. 



The first condition was secured, by performing all of the ex- 

 eriments in a large lecture-room, with all the doors and win- 

 ows closed. To secure the second condition, I employed a por- 

 tion of the apparatus belonging to a large solar microscope, con- 

 sisting of the reflecting mirror, the condensing lens and tube, 

 together with the mechanical arrangements for adjusting the 

 direction of the light As the condensing lens was upwards of 

 four inches in diameter, I hoped to exaggerate enormously what- 

 ever effect the light might exert, by concentrating it on a com- 

 paratively small area. Inasmuch as the aperture in the window 

 through which the light was admitted, was completely closed by 

 this arrangement, the exterior agitations of the atmosphere were 

 not felt in the room ; while the pencil of light, thus thrown on 

 the flame^ traversed it, as well as the surrounding air, without 

 irnparting a sensible amount of heat to the latter. 



I used the best wax-candles^ (as they are called in the shops,) 

 four to the pound, costing about 15 cents apiece.* By allowing 

 them to burn a sufficient length of time to form a well-defined 

 cup for the melted wax, and carefully turning the wicks so as 

 to render them self snuffing, the combustion was found to go on 

 with remarkable uniformity in a calm atmosphere. The rate of 

 burning was determined in the following manner: — A portion of 

 candle, three or four inches in length, was secured to the bottom 

 of one of the scale-pans of a tall balance and ignited; after 

 allowing it to burn for ten or fifteen minutes, so as to secure a 

 steady flame of constant size, it was nearhj balanced by adding 

 weights to the opposite scale-pan,. allowing a slight preponder- 

 ance to the candle-pan. In a short time the equilibrium w^as 

 established by the burning of the candle;— the precise tiTue at 

 which the balance indicated a condition of equilibrium was accu- 

 rately noted. Next, a given weight, (say 60 or 100 grains,) v:z3 

 withdrawn from the weight-pan, and the time of restoring the 



* Prom the close approximation to identity in the rate of consumption, it i.^ prob- 

 able that these are the same as Dr. Ure'a " genuine wax-candlea" He found the 

 consumption to be, "upon an average of many experiments, 126 grams per hour. 

 (Diet, of Arts, Manuf. and Mines, 4th edition. Article, " Illummation, Cost of/') My 

 exp«riments gave respectively. 136'7, 125 4, and 124-7 grains per hour. Other kinds 

 of candles burn at a much more rapid rate. 



