[ i88 ] 
ten or twelve Hours before the apparent Change of 
Weather happens, as this has done fince I got it 
finifh'd ; it may very much aflift to form a true Judg- 
ment on the impending Changes, when the Wind is 
in or near the Eaft or Weft Point, when the Baro- 
meter is of little or no Service. • * 
I obferve, that Heat and Cold have a confiderable 
Power of lengthening and Ihortening the Deal Rod, 
as well as the Moifture and Drynefs of the Air s and 
this, atfirft Sight, would induce one to imagine, that 
it would thereby be render’d almoft ufeiefs 5 but it is 
really far otherwife ; for, by placing it near a Ther- 
mometer, it is eafily reftify’d with refpeft to its Ex- 
panfion or Contra&ion, by Heat or Cold, at the fame 
time that it truly fhews the various Degrees of Moifture 
or Drynefs in the Air. In fhort, it is an Inftrument 
made very eafily, of Materials to be got almoft every- 
where, and of little Coft. It is capable of being fervice- 
able either by Sea or Land, and may be placed in any 
Direttion. 
I have lately finifhed one of thefe Hygrometers, 
the Bar whereof is but a Foot in Length, yet, by 
making the two Levers of Metal, I eafily make the 
End of the fecond Lever rife and fall 8 Inches. At 
this Size it becomes portable, and anfwers the End 
or Purpofe as well as the other. I am, 
‘Dear Sir, 
Tour mojl obedient Servant, 
Wm. Arderon., 
Since 
