Account of an Experiment Made with a Thermometer, Whose Bulb was Painted Black, andExposed to the Direct Rays of the Sun: In a Letter from Richard Watson, D. D. RegiusProfessor of Divinity at Cambridge, and F. R. S. to Mathew Maty, M. D. Sec. R. S.Author(s): Richard WatsonSource: Philosophical Transactions (1683-1775), Vol. 63 (1773 - 1774), pp. 40-41Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/106135 .

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VIt. Sccvant ty4 47} Expert made t'th a 7Jhermomzezer, ^hoJe B>lb qQvS pozinted ffilack, and expofed to the direS Weys ef the Ssa. 1S a Let¢r fioz Richard Watfon, D. D. Rgiss Profor of Dnity vt Cambridgey afz F R. ASt. to Mathew

.

^/faty, AI. 1). (9ec.-2. S.

[IeverXham, September I 8, 1 7 7 sg

DEAR SIR

t)te.la sec, I U R I N G the hot weather, a1vhic}

I772. we had in the lateer end of June

and the heginning of July la{lt I tnade an experi"- xnent at Cambridge) which 1 then thought no more vt, but which an accident llath brought to my mind again; and I now Yenture to fend you an account of it7 in hopes that fome of your philoScaphical friends will take the trouble of proSecuting it. I expoSed the bulb of an excellent thermometer to the direEt rays of the Surl, when the iky was perfedtly free from clouds: the nlercury rofe to lo8°of Fahrenheit's Scale, and continued flationary. A fancy Rruck mes to give the bulb a black covering; this was eafily effeded by a camel's hair penctl and Indian ink; the

mercury

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[ 4t ] tnercury funk a few degrees during the applicatinn of the coating, and the evaporation of the water; but prefently after roSe to I I 8°, or X a° in conSequence of the black coat with wllich- I had covered that ;?art of the bulb which was-:expoSed to ehe Sun. If the bulbs of feveral correEponding thermometers were painted crf different colours, and expoSed at the Eame time to the Sun, for a given period, fome congeAures, re- fpedring the diEpo&tion of the feveral primary colours for receiving and retaining heat, might be formeds which could not fail of being, in fome degree, isl- tereIling.

I am,

DEAR SIR,

Tour mo& obedient ferarantt

Richard Watfion.

vOL. LXlil VIII. aq

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