[ * 3 ° 3 
Degree of Warmth of the Weather marked on the 
femicircular Arch. At (h) is a Screw thro' two 
Studs, to draw the great Lever backwards and for- 
wards, as Occafion may be 5 (i) is a Counter-balance 
to the fmall Lever to draw the Hand back when « 
the Brafs Bar fhrinks. See the Figure prefixed in 
the Tab. 
In the Beginning of the Year 1735. I invented, and caufed to be 
conftrudied, a Thermometer on the fame Principles as this : I 
found that a Rod of Brafs 3 Feet long was fenfibly affe£ted by the 
Changes of Heat of the Weather, having one expofed in my Gar- 
den during the hard Fro ft of the Winter 1739 and. 40. And my 
Inftrument was very fenfible with either a Brafs Rod or an Iron 
Rod, when the Bottom of it was placed in a Sand-Heat for chemi- 
cal Ufes ; but I fhall refer the Reader to the Appendix to the pre- 
ceding N°./>.672. & feq. wherein I have given, a full Defcription of 
my Invention, andjthe Reafons why I did not publifh it before ; tho’ 
I have fhewn the Inftrument to Scores of People ever fince May 
1 735. and fent a Defcription and Draught of it to M. Buffon^ Super- 
intendant of the Royal Phyfick Garden at Paris in the Year 1744. 
in order for his laying it before the Royal Academy of Sciences at 
Paris , from which I had fome time before received a Diploma upon 
having the Honour of being appointed one of their Correfponding 
Members. 
C, Mortimer.. 
E R RATA. 
Page 1. l.g. for Febr. 14. read Jan. 7 and 14. P. 27. 
in the Column exprefling the Nutation, 
1729. Sept. 8. for -—6.9 read — 6.4 
1730. Sept* 8. for —3.4 read — 3.9 
