[ 21 ] 
hook, which fattens them to ttaples at different 
heights ; one of the branches is two inches long, 
and the other four inches, excluttve of putties; by 
which means the balls, when let fa] 1 are direded to 
different parts of the furface they ttrike upon. 
The lead cittern is of an oblong form, that the 
matter therein contained may, at the fame time, re- 
ceive two diftind imprettions ; either when balls of 
different weight are let fall, or the fame ball is let 
fall from different heights; its length is fix inches, 
its breadth four inches, and its depth two inches. 
The matter I have found beft fuited to the pur- 
pofe is ft iff clay, tempered in fuch a manner as to 
be fmooth and uniform, with the fame reduced to 
powder, after having been baked in an oven, as alfo 
after having (by a ttill ttronger heat) been converted 
into brick. 
The cittern is by turns filled with thefe different 
materials, which are to be clofely and uniformly 
prettied down, fo as to leave the furface quite level : 
in effeding which, great caution is required, more 
particularly in regard to the powders; as they will 
not dittindly retain the imprettions, unlefs they have 
forne fmall degree of moifture, or be very clofely 
prettied down ; in both which cafes they acquire fuch 
a degree of cohetton, as of courfe mutt render the 
experiments more or lefs imperfed. 
Things being thus prepared, in order to try the 
neceffary experiments, I ttxt the ttaples, and by their 
means the branches, at the following heights, viz. 
two feet, four feet, and eight feet ; the refult of 
which experiments was as follows. 
When 
