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INTRODUCTION 
The observations now finally published in this volume were made by Professor Peters, during the decade 
beginning in i860, with the 13-inch Spencer refractor of the Litchfield Observatory of Hamilton College, at Clinton, 1 
N. Y. They were prepared in tabular form by their author for publication, and his 412 pages of manuscript tables, 
with some minor omissions, served the printer as copy. It is supposed that Dr. Peters also wrote an introduction 
describing the methods of observation and reduction, but unfortunately this seems to have been hopelessly lost. The 
fourteen original notebooks entitled, “ Observationes astronomicae originales Maculae Solis,” are preserved in good 
condition. These contain for each date a pencil sketch of the appearance of the spots on the sun’s disk (of diam¬ 
eter about 11 cm), presumably copied from the larger sketch made on the projection screen. They also record the 
readings from the chronograph sheets and the declination scale, together with the clock error. 
There were also preserved the 312 sheets of reductions, representing the logarithmic work involved in deriving the 
heliographic latitude and longitude. These also show what reduction quantities, calculated from the adopted ele¬ 
ments of the sun’s rotation, were used each day, but they do not state whence the elements were derived. The author 
doubtless computed tables for his own use in the work, but they have not been found. Investigation has shown that 
he employed for the longitude of the node and the inclination the values derived by Carrington from his long series 
of observations, and recommended by him for future adoption, viz., N = 73°4o' for 1850, 1 = 7° 15'. Dr. Peters 
employed a different period and a different epoch from those of Carrington, and reckoned his longitudes in the oppo¬ 
site direction. 
In order to give, in the author’s own words, a general description of the procedure followed in the observations, 
the editor has translated the following article by Dr. Peters, which appeared in Band 64, pp. 209-213 (1865), of 
Astronomische Nachrichten. 
“In the observations which have been made here since May i860 on the phenomena of the solar surface, the 
principle was adopted of measuring as far as possible everything of a measurable character that appeared on the solar 
disk. Therefore in the first instance the co-ordinates were determined of all the visible spots on each date, and these 
determinations were extended to all the isolated dots and the principal members of groups; also, indeed, to many 
faculae of definite form. For spots of considerable extent the dimensions of the umbra and penumbra were micro- 
metrically determined, generally in the direction of declination and right ascension. An accurate sketch was always 
prepared before the observations and was a necessary auxiliary, partly for convenience as a reference map during the 
observations and partly for the comparative study both of the changes in the forms of the spots and the arrange¬ 
ments of the components of the groups, as well as of the intensity of the outbursts and their relative positions 
and sequence. In the winter months observations were made on every favorable day; but in summer, when fair 
weather can be more safely counted on, every second day was made the rule, inasmuch as this was in general suffi¬ 
cient for keeping the spots under watch in their different stages; and, moreover, the use of the refractor for the obser¬ 
vations at night always required a somewhat disturbing exchange of the attachments at the eyepiece. 
“ For the observation of the sun the image was projected on a screen which, firmly attached to the refractor, shared 
in its motions. At the lower end of the large tube of the telescope two wooden rings were put on at some distance 
apart; each having four corresponding holes through which wooden rods, only slightly elastic, projected about one 
and a half feet. The projection board was fastened in notches cut in these rods at the same distance from the eye¬ 
piece, and was held in place by the springing of the rods. This not only assured the perpendicularity of the plane 
of projection with respect to the optical axis but it also prescribed that the distance of the plane of projection from 
the eyepiece was always the same when the latter was drawn out to a definite mark corresponding to the sharpest 
image. To the board was attached a rather stiff sheet of paper on which had been drawn two systems of parallel 
lines crossing each other at right angles. A single pin, passing through the center of these lines, attaches the paper 
at the point where the center of the image of the field of the telescope falls. By turning the sheet around the pin, 
the lines can thus be made parallel to the directions of declination and hour angle. It is only necessary for this pur- 
^ pose to let the sun’s limb, or any distinct spot, run across parallel to one of the system of lines, preferably along 
1 Latitude =43° 3' 17" 
Longitude = 5 h i m 37?5 W. 
103794 
