EGR ee 
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of observing contacts at the Sun’s limb. 371 
Our station was at Burlington, Iowa, a few miles north of , 
the central line, where the duration of the totality was 2 min- 
utes and 50 seconds. The air was perfectly clear, without cloud 
or haze ; the thermometer during the Eclipse ranged from 76° 
to 67°, and the barometer from 30™140 to 30™065. The wind 
was from the N.W., but very gentle. 
he spectroscopic combination employed, was compiled for 
the occasion from various instruments belonging to Dartmouth 
College, and differed so much in the relative proportion and ar- 
rangement of its parts from those hitherto used, that a brief 
description is perhaps neccessary. 
he telescope which formed the solar image was a comet- 
seeker by Merz & Son, of 4 inches aperture and 30 inches focal 
length. An ordinary Huyghenian eye-piece enlarged the image 
so that when it fell upon the slit of the spectroscope at a dis- 
tance of 5 inches, it was 24 inches in diameter. e use of an 
eye-piece gave an easy means for securing the accurate focus of 
the limb at the slit, an adjustment of great importance. 
spectroscope proper had telescopes of 24 inches aperture and 
162 focal length (by Alvan Clark). The eye telescope was pro- 
vided with an eye-piece magnifying 18 times, and a wire mi- 
ee 
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into sectors of 10° by lines radiating from the center. This 
es 
The spectrum was formed by a train of 5 prisms of 45° each, 
with faces 23 by 33 inches. They gave a dispersion of about 
18° between A and H, with a total deviation of about 165° for 
the D line. The box which contained them was so connected 
ie 
sun’s limb, or of bringing any desired portion of the limb to 
lit. ; 
