OF ARTS AND SCIENCES. 171 



however, will seldom be consulted in any use to which they are put, 

 and .probably nevel* in discussing observations of the zodiacal light. 

 From the longitude of the zenith derived from these tables, the longi- 

 tude of the Sun (from Table III.) is to be subtracted when the 

 "elongation of the zenith" is required for an evening observation. 



Table X. contains the results of measurements made upon the 

 charts representing the evening observations published by Jones in 

 his large work referred to in the preceding discussion as " Jj." The 

 numbers in the first column refer to the charts employed. The date 

 in the second column, and the latitude in the fourth, are also taken 

 fi'om Jones, south latitudes being here expressed in Italic figures. The 

 longitude of the Sun in the third column, and the quantity t in the 

 fifth {t signifying the hour angle of the north pole of the ecliptic), 

 are taken from Table III., with the aid of the times of observation 

 recorded by Jones, which can accordingly be approximately repro- 

 duced by means of Table III., in case they are desired by any reader 

 who cannot consult the original work. These data are followed by 

 two columns giving the respective elongations of the vertices of the 

 " Stronger " and '* Diffuse " Lights observed by Jones. These elonga- 

 tions were measured from the place of the Sun as given on most of 

 the observer's published charts. In some cases, this place falls beyond 

 the limits of the chart, and Jones then adds a note giving the longi- 

 tude of the Sun which was employed in the measurement. The next 

 six columns contain the north and south latitudes of the boundary of 

 the " Stronger " Light at the respective elongations 30°, G0°, and 90°. 

 These elongations were found upon the charts in the same way as 

 those of the vertex. When the northern boundary lies south of the 

 ecliptic, or the southern boundary north, the measured latitude is re- 

 garded as negative, and is expressed in Italic figures, which are used 

 throughout these tables as a substitute for the negative sign. The 

 last six columns give the corresponding figures for the "' DiS'use " 

 Light at the elongations 60°, 90°, and 120°. All the measurements 

 made upon the charts were merely approximate, and they have not, 

 in general, been revised. They are believed, however, to have been 

 made with sufficient care for the purpose in view. When the boun- 

 daries drawn upon the chart terminated near the longitude at which 

 the measurement was to be made, they were occasionally extended 

 by estimate in order to obtain a latitude, but the number of these 

 estimates forms a very small proportion of the entire number of 

 entries. When an unusually large number of observations were 

 made upon a single evening (as on occasions when " pulsations " in 



