This 



'his is the only test and the only requirement for which some 

 means of rectification has not been provided for the engineer. Our 

 method of mounting with the swivel adapter on a carefully centered 

 "solar table", provides a very ready, reliable and accurate means of 

 applying the attachment to the instrument. The casual mounting 

 of the solar, whenever desired for use, probably centers the attach- 

 ment within one or two thousandth of an inch. Repeated tests on 

 rigid inspection have shown an absence of an appreciable error in 

 this respect, and for solar work this degree of accuracy is beyond 

 all requirements in the case. 



In mining surveys the perfect centering of the auxiliary sight 

 line, for the prolongation of shaft alignments, is an unconditional 

 desideratum. We consider this construction falls well within the 

 necessities up to the limitations imposed by the application of so 

 small a telescope to this particular purpose. With an aperture of 

 19mm and a magnification of X12, the light grasp and penetration 

 are confessedly unsuited to the more extensive surveys in deep and 

 smoky pits. 



Direction for the Preparation of the Daily 

 Declination Settings 



The Ephemeris Tables give the daily declination of the Sun 

 for Greenwich, Mean Noon. Since all points in the U. S. are west 

 of Greenwich by 5, 6, 7 or 8 hours, the declination found in the 

 ephemeris is the declination for the place of observation for 7, 6, 5 

 or 4 o'clock a. m. of the same date, as shown by the clock dials in 

 the map, occurring between pp. 163 and 164. In Canada the differ- 

 ence in time ranges between the 4th and 9th hour but most of 

 Mexico lies within the 7th hour correction belt. 



The column headed Refraction Correction gives the mean 

 refraction correction to be added to the declination for any 

 point whose latitude is 40. If the latitude is more or less than 

 40, the tabular corrections are to be multiplied by the correspond- 

 ing coefficient given in the Table of Latitude Coefficients. 

 Thus in latitude 30 the refraction corrections are 65-hundredths 

 of those given in the Ephemeris, and if the latitude is 50 the tabular 

 corrections for 40 are to be multiplied by 1.43, etc. 



Refraction correction for declination may also be used with 

 reasonable accuracy as the refraction correction in altitude, the 

 altitude being changed to its equivalent in hours. Thus in the 

 example, p. 155, the Ref. Cor. for 9 h., 41 m., 50 s. at Lat. 41 28' 

 48" for Mar. 3rd., (see Eph. Tab.) is approximately that for 2 l / 3 

 hrs. at 40 or 1' 16". If we were to calculate the correction 

 from the table, p. XXI, Apx., for Alt. 33 32' 30", we have - 1' 28". 

 Correct this by -f 7" for parallax, we have 1' 21", a difference 

 of only 5" in the two methods. 



164 



