CONTENTS. IX 



134. Vapor pressures of solutions of salts in water 149 



135. Pressure of aqueous vapor at low temperatures . . . . . 151 



136. " " " " o to 100 C (Broch) 152 



137. " " " " 100 to 230 C (Regnault) . . . .153 



138. Weight in grains of aqueous vapor in a cubic foot of saturated air . 154 

 139- " " grammes of " " " " " metre of " " . 154 



140. Hygrometry, vapor pressure in the atmosphere 155 



141. " dew-points ......... 156 



142. Relative humidity .......... 158 



143. Values of 0.378*? in the atmospheric pressure equation h=.B 0.3781?. 159 



144. Table for facilitating the calculation of ^760 ..... 160 



145. Logarithms of ^760 for values of h between 80 and 800 . . . 160 



146. Values of 1-1-0.00367 t\ 



(a) for values of /between o and 10 C, by tenths . . . 162 



(b) " " " " " 90 " +1990 C, by tens . . 163 

 (f) logarithms for t " 49 " +399 c bv units l6 4 

 (d) " " 400 " 1990 C, by tens . . .166 



147. Determination of heights by the barometer ...... 167 



148. Barometric pressures corresponding to different temperatures of the 



boiling-point of water : 



(a) Common measure . . . . . . . .168 



(<) Metric measure ......... 169 



149. Standard wave-lengths : Fabry-Buisson's iron arc lines . . . 170 



150. " " " red cadmium line 170 



151. Stronger lines of some of the elements . . . . .170 



152. Rowland's standard solar wave-lengths (also corrections) . . . 171 



153. Kayser's standard iron arc lines (also corrections) .... 174 



154. Wave-lengths of the Fraunhofer lines . . . . . . .176 



155. Photometric standards .......... 177 



156. Sensitiveness of the eye to radiation of different wave-lengths: low 



(threshold) intensities . . . . . . . . .178 



157. Sensitiveness of the eye : greater intensities . ..... 178 



158. Sensibility of the eye to small differences of intensity (Fechner) . .178 



159. Solar energy and its absorption by the earth's atmosphere . . . 179 



1 60. The solar " constant " of radiation and temperature of sun . . . 179 



161. Distribution of intensity of radiation over solar disk . . . . 179 



162. Relative intensities of sunlight and sky-light . . . . 179 



163. Indices of refraction of Jena glasses 180 



164. MM !8o 



165. " " " " " " temperature coefficients . . 180 



166. " " " " various alums 181 



167. " " " " metals and metallic oxides : 



(a) Kundt's experiments 182 



(b) Du Bois and Rubens' experiments . . . . . 182 

 (<r) Drude's experiments 182 



168. Indices of refraction for rock salt 183 



169. " " " " " " temperature coefficients . . .183 



170. " " " " sylvine 183 



