and the Mode of its Communication. 81 
having varnished them, within and without, with spirit varnish, 
I covered them, within and without, with fine wove writing-paper, 
and then gave the paper three coats of the same varnish. I then 
perforated the bottoms of these boxes with round holes, just large 
enough to admit the neck of the instrument, and the cylindrical 
projection at its bottom ; and then inverted them over the two 
ends of the instrument, filling the boxes at the same time with 
eider-down. 
These boxes were fixed and confined in their places, by means 
easy to be imagined ; and, in order to confine the heat still more 
effectually, each of the boxes was covered on the outside with a 
cap of fur, as often as the instrument was used ; as was also 
that part of the neck of the instrument which projected above 
the box. 
Two of the instruments, which I shall distinguish by the 
numbers i and 2, were covered up at their ends in this manner : 
the other two instruments, No. 3 and No. 4, were left in the 
state represented by the Figure 1 ; that is to say, the ends of their 
cylindrical bodies were not covered with permanent coverings. 
In each experiment, two similar instruments (No. 1 and No. 2, 
for instance, or No. 3 and No. 4) were used, the one naked , 
and the other covered; and, as the naked instrument always 
served as a standard, with which the results of the experiments 
made with the other were compared, it is evident, that this ar- 
rangement rendered the general results of the experiments much 
more satisfactory and conclusive than they could possibly have 
been, had the experiments made on different days, and with 
various kinds of covering, been made singly, or unaccompanied 
by a fixed and invariable standard. 
The experiments were made, and registered, in the following 
mdccciv. M 
