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[[circled] 130 [[ circled]]
Jany 4th 1845 | [[underlined]] Heat of Spots on the Sun [[underlined]]
Saturday

In one of the late Nos of the Annales de Chimie et Physique, there is a paper on the subject of the diminution of heat during the appearance of solar spots. In looking over this article, I was struck with the ease [[insert]]with[[insert]] which the question of the heat from these spots could be determined by the use of the thermo-electrical apparatus.

 Sir W Herschell thought that the spots were hotter than the bright part of the sun, while the investigations of the author of the paper in the Annales would seem to show that the spots were cooler from the fact that in the years where the greatest number of them appeared, the mean temperature of different parts of the Earth was [[insert]]slightly[[insert]] less.

He determined this by grouping the periods in which the spots were the most numerous, but little reliance can be placed on observations of this kind, for although the spots may be [[measurably?]] colder, yet the difference is probably so small, that it cannot be determined with any degree of certainty, as will be evident in comparing the area of the spots with that of the whole disc of the sun.

Yesterday morning, Mr Alexander announced to me the appearance of a very large spot on the sun of which he had taken the measurement, and found it to exceed the Earth in magnitude. He then agreed to make an experiment in reference to the heat of this spot. We did not however get fully prepared before the disappearance of the sun under a very extensive surface of cloud. This morning however, the sky was remarkably clear for this season of the year, and we accordingly proceeded to make the attempt. For this purpose, the Fraunhoffer telescope, belonging to the college, was brought

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[[circled]] 131 [[circled]]
Jany 4th 1845 | [[underlined]]Spots on the Sun [[underlined]]

from Mr Alexanders house, and placed in my  little room at the Hall, the window being darkened by green baize, the end of the telescope being suffered to project out of the window. A very distinct and beautiful image of the spot was thrown on [[strikeout]] the [[/strikeout]] a screen of about 2 inches in diameter, [[?]] the umbra. The black part of the spot was about 3/4 of an inch in diameter, a little larger in one direction than in the other. Its form was something like this: see margin, p 139.

[[image of experimental set-up with telescope and window]]

The arrangement of the apparatus is represented in the above sketch. a the telescope, w the window, p the thermopile, s a paper screen with a hole in it of the size of the pile - the screen was fastened to the end of the pile by a little soft beeswax, g-the galvanometer supported on a shelf let into to the wall at one end, so as to be steady and not movable with the [[?]] of the floor. On the top of the [[insert]]glass[[/insert]] cylinder which contains the apparatus, was placed two magnets furnished by the maker of the instrument, which could be opened or shut at pleasure, and these were intended to change the zero point of the apparatus, and render the whole more [[?]].

Transcription Notes:
"Annales de Chimie et Physique" is a French scientific journal Sir W Herschell -> Likely Sir William Herschel (Only one L) Fraunhoffer -> Likely Fraunhofer (Only one f)