64a 



To use the solar attachment, screw the equatorial adapter upon the central post, 

 level up the transit by means of the plate levels, and assuming that all the ad- 

 justments of the transit and those of its motion in vertical plane have previously 

 been verified, attach the counterpoise and the auxiliary telescope to their screw- 

 studs as already explained, bring the main telescope level-bubble to the middle 

 of its tube, when the zero of the vertical circle should coincide with that 

 of its vernier. Level up the equatorial adapter by revolving it, by means of 

 its level and the two milled-headed screws acting against the opposing springs in 

 the lower plate provided for that purpose. This is necessary in order to make 

 the polar axis truly at right angles to the line of collimation of the main telescope. 

 This adjustment once properly made need only be repeated for verification of 

 adjustment from time to time as deemed necessary. The two telescopes should 

 be placed in the same vertical plane by bisecting with both telescopes some 

 distant object. When the polar axis is clamped, set off on the vertical circle 

 the declination and refraction of the day and hour of observation ; bring the 

 auxiliary telescope into a nearly horizontal position and clamp the declination 

 axis tightly to the upright by means of the inner milled-headed nut, previously 

 taking care that the stud between the two opposing screws shall be nearly in the 

 center. Place the striding level upon the auxiliary telescope and by means of 

 the two opposing screws place the bubble in the center of its tube and then re- 

 move it. The two telescopes now occupy a position with each other equal to 

 the declination and refraction of the day and hour of observation. Set the 

 vertical circle to correspond to the co-latitude of the place of observation and the 

 solar attachment is ready for work. 



The wire arrangement in the auxiliary telescope is a square somewhat smaller 

 than the disk of the sun which is illustrated in diaphragm D on page 168. The 

 outer wires forming the square are equi-distant from the horizontal and vertical 

 central wires and parallel thereto. They are very coarse to distinguish them from 

 the wires marking the line of collimation of the telescope, to avoid mistakes on 

 the part of the observer when the auxiliary telescope is used in the mine. 



The striding level will prove a valuable adjunct for the setting of the auxiliary 

 telescope when used as a side telescope to read the same level line as the main 

 telescope. 



The equatorial adapter being in part made of aluminum and of brass, weighs 

 only nine ounces, the same counterpoise used for the auxiliary telescope may also 

 be used for the equatorial adapter by the exercise of proper care. 



The observations with this solar attachment are exceedingly simple to make. 

 The equatorial adapter raising the auxiliary telescope considerably above the ver- 

 tical circle, observations can frequently be made, if desired, without the use of a 

 prism, by simply screwing the colored glass furnished with the instrument upon 

 the eye-piece. 



The observer should set the tripod firmly, giving the legs an unusually wide 

 spread. 



Observation for Meridian with the Berger Solar 



Attachment. 



Written for this catalogue by GEO. L. HOSMER, Massachusetts Institute of Technology. 



CALCULATION. 



Before beginning the observations the following computations must be made. 

 1. Take from the Nautical Almanac (table II, for the month) the sun's "apparent 

 declination," for Greenwich Mean Noon of the date of the observation. If it is 

 north prefix a -f sign, if south, a sign. 2. On the same line, in the next 

 column to the right is the "difference for one hour," with the proper algebraic 

 sign before it. 3. The local time corresponding to Greenwich Mean Noon may be 

 found by subtracting the west longtitude of the place from 12h, e. g. at the 75th 

 meridian, this would give 7h A.M.; at the 90th, 6h A. M., etc. 4. Next compute 

 the declination for each hour by adding algebraically the "difference for 1 h" 

 to the decimation for the preceding hour. 5. Next correct each of these declina- 



