XXXVIIL 
OBSERVATIONS. OF THE SOLAR ye oN SEPT. 17, 1841, 
MADE AT NANTUCKE 
_ BY HON. WALTER FOLGER, Jun. 
Communicated in a letter to Nathaniel Bowditch. 
¢ TeSkeesh: 1s att 
THE, telescope used j in this observation is a three feet achromat- 
ic, to which I have fixed a micrometer, composed of two screws that 
pass through the eye-tube, so that their points meet in the centre of 
the focus of the eye-glass. On the end of the screw without the tube 
is a circular plate, divided into 10 equal parts by diameters drawn on 
the plate, and: is-sofixed, that the first division of each: screw-head 
shall correspond with a line drawn on the outside ‘of the tube, when 
the points meet in the centre of the focus. The divisions, being made 
to coincide with the lines drawn on the tube, will show the tenth parts 
of a turn of the screw, which is of a very fine thread, such for exam- 
ple as are made use of for a watch; and it is not dificult to estimate 
a tenth part of one of these divisions, which will show +45 of a turn of 
the screw. By the mean of a number of measurements of the sun’s 
diameter, I found 0°9294 turns of the screw would answer to one 
minute. 
_ September 13d. 104. 34’ 54”-5 A, M, mean time, by the mean of 
four altitudes taken by reflection from a surface of molasses, I found 
the clock to be 2’ 11-25 too slow for mean time. In the afternoon 
the wind blew from the westward so strong that I could not make any 
observations. On the 17th at 8, 50’ 23”-1 A. M. mean time, by the 
mean of ten altitudes of the sun I found the clock too slow for meam 
time 5’ 21725. In the afternoon the wind prevented me from ob- 
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