OCT. — MAR. 1858-59.] Report of the Magnetic Survey. 353 





Schlagintiveit. 



Hypsometer 

 No. 5. 



Gubbins. 

 In glass cylinders. 



Black bulb 

 exposed 

 free. 



12-0 . . | 

 1-15.. j 

 1-20.. 



1- 45.. | 



2- 35 . . | 



o « 



88 58 C. 

 191 44 F. 



90 13 C. 

 194 23 F. 



90 oO U. 

 194 54 F. 



86 10 C. 

 186 98 F. 



80 60 C. 

 177 08 F. 



o > 

 190 5 



Disturbed by ap- ) 

 proaching too near, j 



189 5 

 188 0 

 185 0 



1260 



127- 1 



128- 5 

 119-0 

 122-0 



When the hot winds are very violent, they diminish the power 

 of insolation very much by the quantity of dust they raise, which 

 very often, like thick aqueous clouds, completely hides the posi- 

 tion of the sun, and sometimes even produces a darkness like the 

 thickest fog. I had occasion to notice a particular coloration of 

 the sun during dust-storms, which is, I think, quite a regular 

 phenomenon accompanying them, when the air has reached a cer- 

 tain degree of untransparency. 



In fogs the disc of the sun is red, or at least of a decided red- 

 dish tint, when sufficiently darkened to be looked at without a 

 dark glass. In dust-storms the sky has also, as in fogs, a decid- 

 edly reddish color, which in this case is that of the dust itself, but 

 the sun's disc is blue, a phenomenon evidently connected with the 

 suspension of solid particles in the air.* I observed this color 

 best on the 6th of April at Futtehpore. The hot wind lasted from 

 12-45 to 6-10 p. m., and stopped very suddenly after sun-set. The 

 sun was very much obscured as early as 1 p. m., and showed 

 then the blue appearance so decidedly, that it looked like the sun's 

 disc seen through a dark -blue glass, the shadow of a thin cylin- 



* A similar dust- cloud passing perhaps at a small height above the 

 ground may explain the blue appearance of the sun mentioned in the 

 Second Edition of Sir John Herschel's Astronomy. 



