74° − 32° = 42°.00305 × 42 = .128 and 30.597 − .128 = 30.469 the correct height.
When the temperature of the mercury is lower than 32°, the temperature is to be subtracted from 32°, and the product, obtained as before, is to be added to the observed height. Thus, let the barometer be as before, and the temperature 15°: then 32° − 15° = 17°; .00305 × 17 = .052, and 30.597 + .052 = 30.649, the correct height.—Jameson’s Journal, 1827, p. 378.
13. Diamond Lenses.
I am, Sir, yours, &c.
G. DAKIN.
Tringham, Norfolk, July 9th, 1827.
14. Sapphire Lenses for Single Microscopes.
There is a property possessed by small single lenses formed by precious stones, which is worthy of being commented on: viz. They can be burnished fast into brass rings, and thus safely cleaned and removed at pleasure from one setting to another. The cohesion of glass is too slight to permit this operation, during which it is almost sure to burst into shivers.—C. R. G.
15. On a Method of Securing and Preserving the Rowing Pins in Boats.
