218 Mr. C. Tomlinson on the Supposed Action 



weighing ten grains, and ignited both at the same moment. 

 One piece was placed in a dark room at 67° F., the other was 

 exposed to broad sunshine at 78° F. In five minutes 



The taper in sunshine lost 8^ grains. 



The taper in the darkened room lost 9-j- grains. 

 The taper, divided into inches, was also burnt in the coloured 

 portions of the solar spectrum, when it was found that the time 

 required to burn two inches of taper varied as follows : — 



In the red ray it took ... 8 



In the green ray it took ... 8 20 



In the violet ray it took ... 8 39 



At the verge of the violet it took 8 57 



The conclusion is that the solar rays, in proportion to their 



intensity, have the power of retarding to a considerable extent 



the process of combustion ; and it is supposed that the chemical 



rays act in some way on the portion of oxygen about to combine 



with the fuel so as to delay, if not prevent, combination. 



Supposing in these experiments the taper was so uniform that 

 one inch contained precisely the same quantity of matter as an- 

 other inch, the time occupied in burning was too short to justify 

 so important a conclusion as Dr. M'Keever arrived at, whether 

 the results were taken by measure or by weight. 



Every one engaged in photo-metrical observations must be 

 aware of the difficulty of getting rid of disturbing causes and 

 perplexing results. In comparing candles of the same make, 

 the light is affected both in quantity and economy by a number 

 of small circumstances, such as the warmth of the room, the ex- 

 istence of slight currents of air, the extent to which the wick 

 curls over when burning, and so on. In testing the quality of 

 gas, the standard candle denned by Act of Parliament is a sperm 

 candle of six to the pound, burning at the rate of 120 grains per 

 hour. From such a standard we get the terms " 12-candle gas/' 

 "14- can die gas/' &c. Mr. Sugg, in his ''Gas Manipulation/ 

 has pointed out some of the difficulties in obtaining a uniform 

 standard candle. The wick does not always contain the same 

 number of strands; they are not all twisted to the same degree 

 of hardness; the so-called sperm may vary in composition, one 

 candle containing a little more wax than another, or variable 

 quantities of stearine, or of paraffine ; the candle may have been 

 kept in store a long or a short time; the temperature of the 

 store-room may have varied considerably, and the temperature 

 of the room in which it was burnt may have been high or low. 

 All these circumstances affect the rate of combustion and the 

 illuminating-power of candles, irrespective of the action of light, 

 if such action really exist. 



