2 
Sir Everard Home on the black rete mucosum oj 
surrounding skin. I saw the fish several times, and directions 
were given to send it to me when it died ; but I was not so 
fortunate as to receive it. 
This extraordinary circumstance brought to my recollec- 
tion one not less so. In crossing the Tropic in April, 178 1, at 
twelve o’clock at noon, in a voyage to the West Indies, I had 
fallen asleep upon deck, lying upon my back, having a thin 
linen pair of trowsers on, and I had not slept half an hour, 
when I was awakened by the bustle attending the demand of 
forfeits on crossing the Line, and found the inside of the upper 
part of both thighs scorched, the effects of which have never 
gone off, but till now I could not imagine how it happened, 
always suspecting it to be the effect of the bites of insects ; 
but I never satisfied myself upon that subject. 
The effect of the sun’s rays upon the fish under water, led 
me to suspect the mixture of light and heat to be the cause 
of this scorching effect. 
To ascertain the truth of this opinion, I made the following 
experiments. 
Experiment 1. 
In August, 1820, I exposed the back of my hand to the sun 
at twelve o’clock, with a thermometer attached to it, another 
thermometer being placed upon a table, with the same ex- 
posure. That on my hand stood at 90°, the other at 102 0 . In 
45 minutes blisters rose, and coaguiable lymph was exuded, 
which became vascular under my eye : the pain was very 
severe. 
Experiment 2. 
I exposed my face, my eyelids, and the back of my hand 
to water heated to 120 0 : in a few minutes they became pain- 
