| 
_ plane on the ground as the condensed vapour moves on. 
<n i i tft tC A AC CL CL ALLL LLL ALL LL TL 
Sept. 23, 1886] 
NATURE 
909 
this purpose, as will be seen, it is necessary that two large holes 
be drilled in the upper disk of each pair, so as to allow the 
brass pillars of the corresponding annular disk to pass freely 
through. When the connections are made, the current is led 
through the entire apparatus in such a way that, while the electro- 
magnetic force acting on the one suspended coil causesit to descend, 
_ the electro-magnetic force acting upon the other causes them to 
ascend. ‘The total force tending to disturb the equilibrium of 
the balance is thus exactly four times that due to an equal cur- 
rent circulating in two parallel circles of the same diameter and 
with their planes at the same distance apart. The current- 
strength is estimated from the number of grammes required to 
restore the balance to exact equilibrium, the weights being 
placed into small scale-pans attached to the movable part of the 
apparatus. The electro-magnetic force between each fixed and 
_ the corresponding suspended coil is calculated from the formulz 
given by Clerk Maxwell (vol. ii. p. 308), viz. :— 
= — 27 cos 7{2Fy- (1 + sec*y) Ey} 
where M = the potential energy between two parallel circles, 
each carrying unit current, 
6 = distance between their planes, 
@ = radius of each coil, 
sin ze 
i ——— 
/ 42a + e 
Fy and Ey = first and second complete elliptic integrals to 
modulus sin y. 
In one of the instruments constructed 
a = 10°8 inches, 4 = °566 inches, 
which give 
y = 87°, Fy = 4338053976, Ey = 1°005258587 ; 
from which, if G denote the constant of the instrument and 
g = 981, we have 
This gives for 1 ampere a force = 04818 gramme-weight. 
Besides the one exhibited I have constructed several modifi- 
cations of the instrument, only one of which, however, needs be 
particularly mentioned. In it both the fixed and movable coils 
are replaced by flat spirals of wire, each of eleven turns. Here 
the practical construction is more difficult, and the calculation of 
the constant somewhat more laborious, unless one is content 
with merely integrating over the area of both the fixed and 
suspended spirals. This is, I think, however, hardly legitimate, 
at least with thickish wires, as we thereby suppose that elec- 
tricity is circulating in the insulating spaces between the wires 
as well as in the wires themselves. To avoid this I have actually 
calculated the force exerted by each one of the coils of the fixed 
spiral upon each coil of the suspended spiral. This entails great 
labour, as the elliptic integrals have to be calculated for values 
of the modulus differing very slightly from each other. The 
labour, however, is worth the taking, as the attractive or re- 
pulsive force between two flat spirals is so much greater than 
that between two simple circles. 
_ The Peculiar Sunrise-Shadow 0 Adam's Peak in Ceylon, by 
the Hon, Ralph Abercromby, F.R.Met.Soc.—A great pecu- 
 liarity has been noticed by many travellers about the shadow of 
Adam’s Peak at sunrise. The shadow, instead of lying flat on 
the ground, appears to rise up like a veil in front of the spec- 
tator, and then suddenly to fall down to its proper level. 
Various theories have been propounded to account for this, and 
it has usually been supposed to be due to a sort of mirage. The 
author, in the course of a meteorological tour round the world, 
spent the night on the top of the peak, 7352 feet above the sea, 
and obtained unmistakable evidence that the appearance is due 
to light wreaths of thin morning mist being driven past the 
western side of the mountain by the prevailing north-east mon- 
soon up a neighbouring gorge. The shadow is caught by the 
mist at a higher level than the earth, and then falls to its own 
The 
appearance is peculiar to Adam's Peak ; for the proper combi- 
nation of a high isolated pyramid, a prevailing wind, and a 
valley to direct suitable mist at a proper height on the western 
side of a mountain, is only rarely met with. Any idea that the 
appearance could be caused by mirage is completely disproved 
by the author’s thermometric observations. 
Description of a New Calorimeter for Lecture-Purposes, by 
T. J. Baker.—The instrument consists of two exactly similar 
wee 
Te 
Seer 
metallic air-thermometers mounted side by side with their 
U-shaped thermometer-tubes adjacent, so that their indications 
can be easily compared with each other. ‘The air-vessel of each 
thermometer contains a cylindrical well, in which the substance 
to be experimented with is immersed. Each well is provided 
with a discharging-tube furnished with a stop-cock. ‘The scale 
common to both thermometers is of milk-glass, divided into 100- 
equal parts both above and below zero, and let into the stand so 
as to constitute a translucent window which can be illuminated 
from bebind. By means of this instrument many thermal 
problems can be demonstrated before a large audience. 
On the Distribution of Temperature in Loch Lomond and 
Loch Katrine during the past Winter and Spring, by J. T. 
Morrison, M.A.—The author made observations on the tem- 
perature of these lakes on or about the term day of each month 
from December 1885 to June 1886, in continuation of Mr. J. Y. 
Buchanan’s researches. These included the whole length of 
Loch Katrine and the head and middle part of Loch Lomond, 
the deepest sounding, 99 fathoms, being got near Inversnaid in 
the latter lake. At Inversnaid, from Deceinber till March, the 
water was each month of uniform temperature from surface to 
bottom, the temperatures being— 
December 22, 1885 ... 42'8 
January 21, 1886 412 
February 23, 1886 40°05 
March 23, 1886 39°05 
In the deepest sounding obtained on Loch Katrine, 79 fathoms, 
a similar distribution was met with up till February, the readings 
being— 
December 23, 1885 ... (42°3) u 
January 22, 1886 40°4. 
February 24, 1886 39°0 
And, though the maximum density-point was thus attained in 
February, uniformity still prevailed in March down to a depth 
of 70 fathoms, the readings on March 24 being: surface, 38°°1 ; 
70 fathoms, 38°; 79 fathoms, 38°°7. In April the tempera- 
ture distribution usually found in spring had set in in both lakes, 
the surface being warmest, the bottom coldest, and the tempera- 
ture falling more and more slowly with increase of depth. The 
circumstance of most interest, however, is that the warmth of 
the bottom layer increased monthly over the deepest parts of 
both lakes, as follows :— 
March April May June 
rs) ° ° 
39°4 40°3 40°6 
39°I 40°r 40°65 
Loch Lomond (99 fathoms) 39°05 
Loch Katrine (79 fathoms) 38°7 
This rise is evidently due not to the conduction of heat nor to 
the penetration of solar radiation, but to some drainage or oozing 
causing mixture. This supposition seems necessary also to 
explain the behaviour of Loch Katrine in March. Drainage 
em masse appears to occur chiefly in winter and spring, not in 
summer when the river water and the lake surface water are 
much warmer than the deep water of the lake. The mean tem- 
perature of Loch Katrine probably has a greater range than that 
of Loch Lomond. The shallower parts of the lakes resemble 
the deep parts as to uniformity of temperature up till March. 
But their yearly range is greater. In both lakes the mean tem- 
perature becomes uniform along the whole length about April 4. 
On the Distribution of Temperature in the Firth of Clyde in 
April and Fune 1886, by J. T. Morrison, M.A.—In the latter 
parts of April and June of this year Mr. John Murray, Dr. Mill, 
and the author made serial temperature soundings throughout 
the Clyde district, chiefly with Negretti and Zambra’s reversing 
thermometer. It was found that in matter of temperature the 
waters of the district were divisible into four groups: I. North 
Channel and the plateau south of Arran ; Il. the Arran and 
Dunoon open basins ; ILI. the deep-sea lochs ; IV. the shallow. 
sea lochs. The average temperature in each group at every 
depth was calculated for April and June, and these averages 
form the basis of this paper. In April in all groups there is a 
deep layer of uniform temperature overlaid by a layer of tem- 
perature rising steadily to the surface. In groups Il., III., and 
IV. the uniform deep temperatures are almost the same, about 
41°-4 F.; in group I. it is 418 F. In June the superficial 
X No sounding made here in December. Above tempz2rature ‘s calculated 
from that of another part of the lake. 
