380 Dr Glover on the Colouring Matter of the 



sent with the heating rays at each advance of time. A refe- 

 rence to the original paper will convince the reader that this 

 assumption is established without sufficient data. 



Most stress has been laid by Sir Everard, and those who have 

 adopted his views, on the seventh experiment. We are told 

 that, on the 9th of September, at 11 a. m., thermometer 90° in 

 the sun, the concentrated rays applied to a piece of black ker- 

 seymere wrapped round the arm, gave no real pain, as it is ex- 

 pressed, during 15 minutes ; and at the end of that time left 

 no appearance on the arm ; whereas, when white kerseymere 

 was substituted, during the same time, and the concentration 

 we are led to suppose being the same, the heat of fi thermo- 

 meter in the sun only 86°, yet blisters were formed. From 

 this experiment, taken along with those preceding, it is sup- 

 posed to be fully proved that although black surfaces rise to a 

 higher temperature than white under the sun's rays, yet they 

 scorch the surface of the body less ; the scorching effect de- 

 pending on a union of the rays of heat with those of light, the 

 latter being supposed, by way of explanation, to be excluded by 

 the black surface. First, I shall state my repetition of the 

 experiment, and then attend to Sir Everard's explanation of 

 his supposed fact. 



I have attempted to ascertain the rise which the absorption 

 of heat by black and white cloths respectively gives to the 

 thermometer ; to compare this observation with the effects of 

 the same cloths under the sun's rays upon the body, and with 

 the effect of the sun's rays on the naked skin. When the ther- 

 mometer stands at about 80° in the sun, the solar rays con- 

 centrated on white cloth over the ball of a thermometer, to a 

 space of an inch and a half in diameter by a burning-glass, 

 caused a rise of the thermometer to 125° in a quarter of an 

 hour. When black cloth was substituted the rise during the 

 same period was to 172°. In five minutes, with the white, the 

 rise was to 108°, with the black to 140° ; and in some experi- 

 ments in a proportion nearer that given by the longer period. 



When the black and white cloths were applied to the skin 

 at the same temperature, and with the same degree of concen- 

 tration, as already mentioned, the black cloth generally caused 

 intense pain in the couise of a few minutes, and on being al- 



