OF ARTS AND SCIENCES. 175 



The remaining tables exhibit a grouping of the observations accord- 

 ing to the principle announced by Jones that the position of the zodi- 

 acal light in latitude differs according to tlie inclination of the ecliptic, 

 as it has been called in the previous tables ; that is, according to the 

 zenith distance of the north pole of the ecliptic. Tables XXIII. to 

 XXVI. inclusive arrange the results here obtained for the work of 

 Jones in seven groups defined as follows : Group 1 includes the 

 observations of 18;>3, June, July, August, and September; and of 

 1854, May, June, July, September, and October. Group 2 includes 



1853, October, and 1854, August and Xovember. Group 3 includes 



1854, April and December. Group 4 includes 1853, November and 

 December; 1854, February and March; 1855, April. Group 5 

 includes 1853, April, and 1854, January. Group 6 includes only 



1855, January, and Group 7, 1855, February and March. The num- 

 bers of these groups are given in the first column of each table from 

 XXIII. to XXVI. inclusive. In Table XXIII. the second and third 

 columns give the mean inclination of the ecliptic and elongation of 

 the zenith derived from Table XIII., allowing equal weight to all 

 the separate observations, so that the weight allowed to the result for 

 each month is proportional to the number of observations for that 

 month. The next two columns give the number of observations of 

 the elongation of the vertex of the " Stronger " Light, with the mean 

 result, allowing all observations equal weight, as before. The re- 

 mainder of the table contains the mean results for the latitude of the 

 boundaries of the " Stronijer " Lisfht, with the number of observations 

 on wiiich each depends, collected from Table XIV. 



Table XXIV. contains similar data for the " Diffuse" Light, from 

 Tables XIII. and XV. In the second and third columns, instead of 

 repeating the inclination and elongation already given in Table XXIII., 

 it appeared more convenient to insert the mean latitude of the ob- 

 server, and the zenith distance of the Sun, this last being derived from 

 the data of Table XXIII. by means of a chart. 



Tables XXV. and XXVI. give for each of the seven groups, and 

 for the " Stronger " and " Diffuse " Lights respectively, the number 

 of observations and the mean result for '- latitude of axis," " half extent 

 in latitude," "displacement," and "contraction," as already explained. 

 These quantities are obtained from Tables XVI., XVII., and XVIII. 



Tables XXVII. and XXVIII. contain a similar series of results 

 for the work of Ileis and Weber. The groups, for Ileis, are as fol- 

 lows : Group 1, May, November, December; Group 2, January, 

 April ; Group 3, February, March. The two observations, one ia 



