126 RUDBERGE ON THE MEAN TEMPERATURE OF THE GROUND. 
/2 Tn. 4- 1| mn. Tm. 
But, if we deduce the atomic weight of 
Tungstic acid from the last analysis, we have, 
26*95 (the whole bases) : 
4 :' 5 Can atom of base) :: 
73*60 fV/ie lohole acid) : 
12*28 (an atom of acid) 
Approaching 12*25 as nearly as can be 
expected from the inaccuracies incidental upon 
experiments. Employing 12*25 then, as the 
atom of tungstic acid, and calculating as before 
we get. atoms. 
Tungstic acid 6*00 or 2*41 nearly 2^ 
Protoxide of iron 2*49 ,, 1*00 ,, 1^ 
Protoxide of manganese 3*50 ,, 1*40 l| 
represented by the formula,/ Tn. -j- la Tn. 
The diiference between this and former 
analysis would lead to the opinion that they 
M^ere different species, since both that of 
Berzelius and the present one agree exceed- 
ingly well, with the atomic proportions 
deduced from the formulae by which they are 
represented. 
Great doubt still hangs about the atomic 
weight of tungstic acid, _ and further experi- 
ments are required to elucidate the subject. 
ON THE MEAN TEMPERATURE OF 
THE GROUND AT VARIOUS DEPTHS. 
By f. Rudberge.* 
At the end of December 1832, three ther- 
mometers, by my suggestion, and at the 
expense of the Academy of Sciences at Stock- 
holm, were put in the ground at that place. 
They were filled with mercury, and were 
compared while in the vertical position with 
an accurate thermometer, so that the influ- 
ence of the mercurial column was provided 
against. The thermometers were placed in 
glass tubes, which were shut at the bottom 
by perforated stoppers, and filled with fine 
sand. The depths at which the balls of three 
thermometers were placed, were one, two, 
and three feet respectively. The place where 
they were buried lies in the middle of that 
considerable plain on which the astronomical 
and now also the magnetical observatories are 
situated. 
The observations began in December of 
the above year; but during the first six months 
they were made only onee a day. After that, 
however, the thermometers were observed 
three times in the day, at 6 a. m. and at 2 
and 9 r. M. As the natural equilibrium of 
temperature would of course be disturbed by 
digging up the earth, and a considerable time 
would be requisite to allow this to return to 
its usual state. I shall here omit the observa- 
tions of the first half year, and state only 
those from the 1st. of July 1833, to the 1st. 
of July 1834. The monthly means of these 
are the folllowing : — 
TEMPERATURE AT THE 
DEPTH OF 
ONE 
TWO 
THREE 
FOOT. 
FEET. 
FEET. 
1833. July .... 
60*548 F 
59*000 
56*966 
August . . 
55*616 
55*456 
55*184 
September . 
53*924 
53*610 
53*474 
October . . 
48*146 
48*344 
49*262 
November 
39*002 
40*316 
42*206 
December. . 
33*458 
35*186 
37*004 
1834. January. . 
29*282 
31*244 
32*720 
February . . 
31*316 
31*964 
32*432 
March .... 
32*640 
33*134 
33*440 
April 
38*041 
37*436 
36*932 
May 
48*020 
46*562 
45*104 
June 
56*570 
54*500 
52*312 
If we lake the mean of the result of each 
thermometer, then will the mean annual tem- 
perature of the ground at Stockholm be. 
At the depth of 1 foot 43-880 
“ 2 feet 43*898 
“ 3 feet 43*906 
Whence it follows that the mean temperature 
of the ground, at least to the depth of three 
feet, is independent of the depth ; and in all pro- 
bability this proposition will be correct for 
all depths, till the point where all variation 
of temperature ceases. 
The table shews, besides, that temperature 
at the end of September and the end of march, 
or at the time of the vernal and autumnal 
equinox, is the same at all these depths. 
Although more observations maybe required 
to settle these two propositions, I have, 
nevei*theless, thought it proper to draw the 
attention of meteorologists to them that they 
may try their accuracy in other places. 
This mean temperature of the earth is greater 
than the mean temperature of the air at 
Stockholm, which is only 42*24 F. 
ASHMOLEAN SOCIETY OF OXFORD, 
1835. 
THE FIRST MEMOIR PRINTED BY 
THIS SOCIETY IS ENTITLED, “ ON 
THE ARCHROMATISM OF THE EYE. 
By the Rev. Baden Powell, A. M^&c. 
It is well known that when rays of light are 
inflected by a lens they undergo a deviation, 
by which they are prevented from concentrat- 
ing in the same point or focus. This aber- 
ration gives origin to the production of colour 
at the foci of lenses, and constituted a great 
imperfection in refracting telescopes until the 
discovery was made, that a compensation for 
the deviation of the rays of light might be 
effected by employing compound lenses. Those 
telescopes in which this improvement was in- 
troduced were termed achromatic. Now, as 
there appears no compensation in the eye 
for this aberration, it is natural to inquire into 
the reason of our seeing objects without pris- 
matic colour. Such is the question which 
Professor Powell undertakes to investigate in 
the present paper. He presents vis first with 
* From Fogg. Ann. xxxiii. 351. 
