AND MOUNTAINS OF N.W. INDIA. XXXIii* 
** With due allowance for the difference of sensibility in the instruments, the above table shews that 
the average diurnal tide of the barometer between the Equator and 30° north latitude, exceeds one-tenth 
of an inch, and that it is progressively greater as the variation of temperature during the day is also 
greater. With regard to the nocturnal tide of the atmosphere, the Calcutta tables afford us no data, for 
want of an observation at 10 p.m., the hour of the supposed maximum at night; all that is indicated 
therein is, that the barometer is constantly ower at sunset than at sun-rise. At the Madras observatory, 
in 1823, a series of horary observations was made for three days in each month, which seems to establish 
the fact of a night-tide beyond a doubt to the extent of .04 inch; when, however, the corrections for the 
temperature of the mercury are applied, this amount is reduced to two-hundredths of an inch, which is 
one-fifth only of the diurnal tide. 
“ The same result is obtained from a month’s horary observations, undertaken by Col. Balfour, at 
Calcutta, in the year 1784. At Saharunpore, also, the existence of a nocturnal tide is equivocal: the 
following table exhibits all that we can gather towards the elucidation of the point in India, expressing 
by minus signs the real tide, or fall of the barometer, from 10 p.m. to 5 a.m., and vice versd.” Mr. 
Prinsep concludes by saying, “ There is still sufficient ambiguity respecting this second tide, therefore, 
to render further inquiry necessary, and it would be desirable to employ a barometer for the purpose, 
which should not require to have any correction applied for the temperature of the mercury ; this might 
be easily effected, by enclosing the barometer tube in an outer tube of the same length, also filled with 
mercury, upon the surface of which the scale might float.” 
Nocturna OscitLaTion of the BARoMETER from 10 P.M. to 5 a.m. reduced to 32° Fahr. 
Mon i ae Pe om a 
January ..seeee. eectan ones ee ae —-004 +034 —-043 +-018 
February Pee eer ert eerste esen eee —*929 +:026 — 009 +009 
PRACT wis Sse ows woe Po bee —-026 +-069 — 008 —002 
BOT ens sao i aceee acew cceen’ — 027 +-008 — 007 +008 
MAY: . wit aide Sass eWiew whee cess — (014 +-020 —020 +005 
SUNG ose cee ke cock cc ee ees es —026 +:012 +-039 +-003 
VOIP sis. Sess Ce ts CER ee TELE — 009 -000 — 005 — 002 
Aupust ee se cetesecccceccveese —-0)28 +014 — 016 —007 
Septemver so i wisi esi F446 wees — 024 +011 +011 —-012 
OCtOBEr 2 oo6 oe cigar see vs ee —-033 +009 — 004 — 021 
November! (issn ccc e cee si ae — 010 +009 +°024 +00] 
December ...-ssccsdseecscese —019 +:027 +015 —023 
Means......+- —021 +020 — 001 — 002 
Saharunpore, as we ove seen, is situated nearly at the head of the great Gangetic valley, in N. Jat. 
29° 57’, long. 77° 32’ E., one thousand miles north-west of Calcutta, in the Doab, or space included 
between the Ganges and Jumna rivers, about twenty miles from the former, and nine from the latter, 
and about thirty miles from the Sewalik or Sub-Himalayan range of Mountains. It is celebrated as the 
station whence the Trigonometrical Survey of the Himalayas was commenced by Capts. Hodgson and 
Herbert (v. p. xii.) It was then calculated by Capt., now Col., Hodgson, to be elevated 1,013 feet 
above Calcutta. Mr. James Prinsep, from my observations, compared with his own, in Calcutta, calcu- 
lated that my house, situated in the vicinity of the Botanic Garden, was as near as possible one thousand 
feet above the sea (Journ. As. Soc., vol. i. p. 29). The characteristics of the climate are mentioned at. 
p. 7, in connection with the vegetation, which is described as being tropical at one season, and partially 2 
European at another, and as having, in consequence, an equally varied cultivation. To display this = 
connection of climate with vegetation, it is desirable to give the temperature, so as to show the rise and fall 7 ; 
of the thermometer ; I have therefore thought it advisable to commence with the month of March, when. 
increase of temperature takes place so rapidly. The thermometer was placed on the northern side ae 
the house, but too near, for the extremes to be accurately observed, rad — the heat | was: ms probably ee 
