57 



C. L, Berger & Sons' Solar Attachment. 



Written for this catalogue by H. C. PEARSONS, C. E., Ferrysburg, Mich. 



The " Solar Attachment," of which the following is a description, is a modification 

 of Pearson's Solar Transit. 



With the view of reducing the weight and cost of this attachment, the declination 

 arc is dispensed with, using, in its stead, the latitude arc for setting ofl' the dec- 

 lination. 



And to attain a greater degree of precision, a small telescope with cross-hairs, and 

 a diagonal eye-piece, have been introduced in place of the lens-bar and focal-plate. 



This attachment is an appliance to the surveyor's transit, for the purpose of 

 finding the astronomical meridian. Combined with that instrument, it becomes 

 purely astronomical in its character indeed, a portable Equatorial, and an Alt.- 

 Azimuth instrument combined, hence a few astronomical definitions seem to 

 be requisite. 



^SSSSs, 



In the accompanying cut, the instrument is represented in position for an ob- 

 servation; and in north latitude (as in these instructions we will suppose the observer 

 to be) the view is as from the west. 



(1.) The line through the vertical axis of the transit represents the pole of 

 horizon, and is called the Vertical. 



The line perpendicular to this represents the Horizon. 



(2.) The transit telescope, having its optical axis in the meridian, and having 

 its south end (whether object-end or eye-end) elevated so that the vertical-arc reads 

 the co-latitude, will have its optical axis in the plane of the equator also ; viz. the 

 optical axis of the telescope will then represent the intersection of the plane of the 

 meridian, with that of the equator. This line is called the Equator. 



(3.) The line perpendicular to the equator, that around which the solar 

 telescope revolves, in following the sun in his diurnal course, is the pole of the 

 equator. It is parallel with the earth's axis, and is called the Polar Axis. 



