50 REPORT—1840. 
or many instruments are to be compared, constant sources of 
heat, natural or artificial, cannot be too carefully sought. Bark 
pits, natural hot springs, even the waste hot-water of steam- 
engines, and the boiling point of some liquids, such as alcohol, 
may be usefully employed*. 
B. Atmospheric Temperaturet. 
34. Under this head we consider the temperature of a given 
spot at different times. These variations are diurnal, annual, 
and those of long period. 
35. A summary of valuable facts on this subject may be found 
in Kamtz’s Meteorologiet and Dove’s Repertorium§. We can 
only point out a few general facts of especial importance. 
36. The general practice in Germany of expressing periodic 
changes of temperature by series of the form 
T=A + Bsin(#+ C) + Dsin (2a + KH) + &c., 
where x is the hour angle, or the fraction of a year, is attended 
with considerable advantages, especially for the purposes of in- 
terpolation ; and if this has sometimes been carried perhaps too 
far, yet the reductions are on the whole very superior to those 
in use in this country, 
37. The value of hourly observations of temperature seems 
now to be fully admitted, and the two-hourly meteorological 
observations connected with the recent magnetic expeditions 
fitted out by the English government, are likely to be of the 
highest importance for science. In the mean time we may quote 
the following important contributions, in addition to those spe- 
cified in the former report. 1. Goldingham’s hourly observa~- 
tions, three times a month at Madras ||. 2. Brandes’s observa- 
tions at Salzuflen (lat. 52° 3! N.), made every hour in the year 
182894. 3. The observations which, at the earnest suggestion 
of the Meteorological Committee of the British Association at 
its first meeting at York, have been so ably and zealously car- 
ried on hourly for seven complete years, under the direction of 
Mr. Snow Harris at Plymouth. The means have been regularly 
- * T have found by the most careful experiments that the temperature of the 
vapour of impure alcohol remains surprisingly steady, which was before re- 
marked by Hugi (Alpenreise, Solothurn, 1830), but it is not the same with 
zther. There are some interesting experiments on the constancy of the tem- 
perature of vapour from saline solutions in the late volumes of Poggendorff’s 
Annalen, especially by Rudberg, xxxiv. 527. 
+ See former Report, p. 210. Mahlmann, p. 31. t Vol. iii. p. 342. 
-§ Vol. ii. p. 1. || Madras Observatory Papers, calculated by Dove. 
§| Archiv der Pharmacie, Reihe ii. Bd. xi. 1, quoted in Poggendorff, xli. 635, 
and Poggendorff’s Remarks, xli. 630. Compare Comptes Rendus (Paris), i. 264, 
and Dove’s Repertorium, iii, 345. 
