Head of the Ganges, 'S&5 
variation must be added to the magnetic azimuth* The diur- 
nal small changes in the barometer were perceptible, the mer- 
cury always falling a little before noon, as in the plains.” 
“ It was remarked above, that the snow on the great bed was 
stuck as it were with rock and rubbish in such a manner, as that 
the stones and large pieces of rock are supported in the snow, 
and sink as it sinks. As they are at such a distance from the 
peaks, as to preclude the idea that they could have rolled down 
to their parent places, except their sharp points had been co- 
vered, it appears most likely, that the very weighty falls of 
snow, which there must be here, in the winter, bring down with 
them pieces of rock, in the same manner as a large snow ball 
would collect gravel, and carry it on with it in its course. Masses 
of snow, falling from the high peaks which bound the snow bed, 
if they chanced to collect more, and to take a rounded form, 
would have a prodigious impulse, and might roll to the centre of 
the snow valley, loaded with the pieces of rock they had involved. 
u It is not very easy to account for the deep rents which in- 
tersect this snow-bed, without supposing it to be full of hollow 
places. It struck us, that the late earthquakes might have oc- 
casioned some of the rents. I never saw them before on other 
snow-beds, except at Jumnotri, where they are occasioned by 
the steam of the extensive range of boiling springs there : per- 
haps there may be such springs here also. They are frequent 
in the Himalaya, and one might suppose they were a provision 
of Nature to insure a supply of water to the heads of the great 
rivers in the winter, when the sun can have little power of melt- 
ing the snow above those deep recesses.” 
Art. IV. — Historical Account of Discoveries respecting the 
Double Refraction and the Polarisation of Light . (Con- 
tinued from p. 1 60. of this volume.) 
Sect. III. — Continued. Account of the Experiments (f Mr 
Benjamin Martin. 
The Second Essay of Mr Benjamin Ma/tin is entitled, 
u Essay II. On the Nature and Wonderful Properties <f 
Island Crystal , containing, 1. The Construction of a Telescope 
