OF ARTS AND SCIENCES. 173 



Tables XIII. to XVIII. inclusive contain monthly means derived 

 from Table X. In order to facilitate any grouping of the months 

 which may appear desirable, the sums of the readings have generally 

 been retained in these tables, the form of which, in other respects, has 

 been largely determined by considerations of convenience in printing. 

 Table XIII. gives the names of the successive months during which 

 Jones carried on his work, preceded by a column of numbers for refer- 

 ence, which is repeated in the subsequent tables without the names of 

 the corresponding months. The third column of Table XIII. gives the 

 number of evenings in each month on which the observations collected 

 in Table X. were made, and in the fourth column are entered the 

 corresponding total numbers of observations. The fifth column gives 

 the mean result for the observer's latitude, expressed in whole degrees. 

 The next two columns contain the inclination of the ecliptic and the 

 azimuth of its north pole, as in the corresponding columns of Table 

 XII. Instead, however, of finding these quantities for each separate 

 observation and talking their means, it was considered sufficient to take 

 the monthly means of the quantities in column t of Tab'e X., and to 

 combine the result with the mean latitude. The mean of the longitudes 

 of the Sun for each month is given in the next column, and this is 

 followed by the elongation of the zenith, the longitude of which was 

 first found from tlie mean values of t and the observer's latitude, as 

 just explained. The last six columns of Table XIII. give the mean 

 elongations of the vertices of the " Stronger " and " Diffuse " Lights, 

 preceded by the numbers of observations and the sums from which the 

 means were derived. 



Tables XIV. and XV. give in like manner, for the " Stronger " and 

 *' Diffuse " Lights respectively, the mean latitudes of their northern 

 and southern boundaries at the various elongations included in Table 

 X., with the numbers and sums used in obtaining the means. 



Tables XVI. and XVII. give mean results at the same elongations 

 for the " latitude of the axis " (as we may call the mean of the latitudes 

 of the northern and southern boundaries), and for half the extent of 

 the light in latitude (the " halbe Dicke " of Schmidt). Italic figures 

 here indicate south latitudes. In obtaining these results, only those 

 observations of Table X. were employed in which both the northern 

 and the southern boundaries had been observed at the required elonga- 

 tions. The results accorditigly differ to some extent from those which 

 would be obtained by the combination of the mean results given in 

 Tables XIV. and XV. 



Table XVIII. gives the mean results for the changes produced in 



