LITERARY NOTICES. 



753 



dam which will be exclusively occupied 

 with sun-observations. 



Carrington's work covered the period 

 1853-1861, and Spoerer's extended from 

 1861 to 1871, and was done on much the 

 same plan. He, of course, confirms the dis- 

 covery by Carriugton of the law which de- 

 clares that the velocity of the rotation of 

 the outer layer of the sun's surface is great- 

 est near the sun's equator and diminishes 

 gradually toward the poles, and he arrives 

 at other conclusions, a few of which we will 

 give, as generally interesting, referring stu- 

 dents of astronomy to the original work. 

 It is well known, from the recent observa- 

 tions (since 1853), that Schwabe's discovery 

 is true that the number of spots on the sun's 

 disk is governed by some periodic cause 

 which produces a maximum number and a 

 minimum number of spots every eleven 

 years. It is probable that magnetism, rain- 

 fall, and temperature, and other terrestrial 

 phenomena, are connected with this period 

 of eleven years, the cause of which is as 

 yet unknown. 



Spoerer has discussed the observations 

 of the spots separately for each half (i. e., 

 northern and southern) of the solar disk. 

 He finds (page 137) that the points of max- 

 imum and minimum frequency of spots are 

 reached earlier in the southern hemisphere 

 of the sun. " While the minimum of the 

 year 1856 still lasted in the northern hemi- 

 sphere, the increase (in the number of spots) 

 had already begun in the southern hemi- 

 sphere, and had here in 1858 reached a 

 maximum," while in the northern hemi- 

 sphere the maximum began in 1860. The 

 mean heliographic latitude of the spots, 

 however, shows "no characteristic differ- 

 ence between the two hemispheres." 



In the eleven-year period (1854-1864) 

 the ratio of the number of spots in the 

 northern hemisphere to the number in the 

 southern was 933 : 1,000 ; from 1861-1871 

 this ratio was 976 : 1,000. The spots on 

 the sun give a means of determining the 

 velocity of the sun's rotation, but the de- 

 termination of this element is complicated 

 by the fact that these spots have a drift or 

 proper motion in longitude. Spoerer finds 

 the angle through which the sun rotates 

 in one day to be 14 16' nearly, while Car- 

 rington determined this element to be 14 



11'; that is, Spoerer fixes the time of the 

 sun's rotation on its axis as 25 days, 5 

 hours, 37 seconds. This mean value 14 

 16' is, however, subject to change, and 

 Spoerer suggests that further investigations 

 may show that the changes which are 

 known to occur in this value may be found 

 to occur earlier in that hemisphere of the 

 sun which has, at the time, the greatest 

 spotted area. This question it will require 

 several eleven-year periods to settle. 



It is to be hoped that these most valu- 

 able researches will be continued, and that 

 America will contribute her full share to the 

 labor. There is a sure reward awaiting in- 

 vestigators in this field. 



The Elevations of Certain Datum-Points 

 on the Great Lakes and Rivers, and 

 in the rocky mountains. by james t. 

 Gardner, Geographer (from the Report 

 of the United States Geological and Ge- 

 ographical Survey of the Territories 

 for 1873). Washington: Government 

 Printing-Office, 1875. 



In this modest pamphlet of thirty pages 

 Mr. Gardner has made a very valuable step 

 toward utilizing a vast quantity of material 

 which has until now been little employed. 

 Every railroad or canal has been located 

 only after one or two lines of leveling have 

 been run between its terminal points, and 

 a mere glance at a railroad map of the 

 United States will show what an immense 

 collection of data exists for the determina- 

 tion of the altitude of any point on any 

 railroad. 



A complete discussion of this has not 

 been attempted, Mr. Gardner's principal 

 object having been to determine the altitude 

 of Denver, in Colorado, above the mean 

 level of the Atlantic Ocean, Denver being the 

 point to which the altitudes determined by 

 the survey of the Territories are referred. 



Incidental to this object, results of great 

 interest have been obtained, a few of which 

 will be mentioned. The material for the 

 work was necessarily of the most varied 

 character and of many degrees of accuracy, 

 from the first trial-lines of reconnaissance- 

 surveys to the final releveling of a finished 

 railroad or canal. Great care was neces- 

 sary in selecting from the reports of chief- 

 engineers and elsewhere the right figures, 

 and in giving proper weights to these when 



vol. vi. 48 



