On HYGROMETERS. bic 
pieces of foft iron, which together equalled one of the 
magnets, were inclofed in,a little box of mahagany wood, 
the grain of whith ran with, and not acrofs, the length of 
the box ; and the box was clofed by a little fhutter of the 
fame wood, the grain of which ran acrofs the box ; and 
the ends of this fhutting piece were bevelled fo as to fit and 
flide in a kind of dovetail groove when the box was to be 
fhut or opened. 
I had been of opinion that good mahogany wood was 
not affected by moifture fo as to change its dimenfions, 
and that it was always to be found as the tools of the 
workman left it. Indeed the difference at different times 
in the fame country, is fo {mall as to be fcarcely in a com- 
mon way obfervable. Hence the box which was made fo 
as to allow fufficient room for the magnets to flide out and 
in freely, and, when in, afforded them fo much play that 
by fhaking the box one could make them ftrike the op- 
pofite fides alternately, continued in the fame ftate all the 
time I remained in England, which was four years, with- 
out any apparent alteration. I left England in Augutft 
1762, and arrived at Philadelphia in O&ober the fame 
year. In a few weeks after my arrival, being defirous of 
fhowing your magnets to a philofophical friend, I found 
them fo tight in the box, that it was with difficulty I got 
them out; and conftantly during the two years I remain- 
ed there, viz. till November 1764, this difficulty of get- 
ting them out and in continued. ‘The little fhutter too, 
as wood does not fhrink length ways of the grain, was 
found too long to enter its grooves, and not being ufed, 
was miflaid and loft ; and I afterwards had another made 
that fitted. 
In December 1764 I returned to England, and after fome: 
time I obferved that my box was become full big enough 
for my magnets, and too wide for my new fhutter; which 
-was fo much too fhort for its grooves, that it was apt to 
falli 
