NATURE 
[Fuly 22, 1886 
of the opposed surfaces to be a few square centimetres. 
To fix the ideas, I shall suppose it to be exactly thirty 
square centimetres. If my sense of force were sufficiently 
metrical I should find that the work done by the attraction 
of the rigidified pieces of water in pulling my two hands 
together was just about four and a half centimetre- 
grammes. The force to do this work, if it had been 
uniform throughout the space of fifty micro-millimetres 
(five-millionths of a centimetre) must have been nine 
hundred thousand grammes weight, that is to say, 
nine-tenths of a ton. But in reality it is done by a force 
increasing from something very small at the distance of 
fifty micro-millimetres to some unknown greatest amount. 
It may reach a maximum before absolute contact, and 
then begin to diminish, or it may increase and increase 
up to contact, we cannot tell which. Whatever may 
be the law of variation of the force, it is certain that 
throughout a small part of the distance it is considerably 
more than one ton. It is possible that it is enormously 
more than one ton, to make up the ascertained amount of 
Hy 
| 
Fic. 1. 
work of four and a half centimetre-grammes performed 
in a space of fifty micro-millimetres. 
But now let us vary the circumstances a little. I 
take the two pieces of rigidified water, and bring 
them to touch at a pair of corresponding points in 
the borders of the two surfaces A and B, keeping 
the rest of these surfaces wide asunder (see Fig. 1). 
The work done on my hands in this proceeding is 
infinitesimal. Now, without at all altering the law of 
attractive force, let a minute film of the rigidified water 
become fluid all over each of the surfaces A and B : you see 
exactly what takes place. The pieces of matter I hold in 
my hands are not the supposed pieces of rigidified water. 
They are glass, with the surfaces a and B thoroughly 
clean and wetted all over each with a thin film of water. 
What you now see taking place is the same as what would 
take place if things were exactly according to our ideal 
supposition. Imagine, therefore, that there are really two 
pieces of water, all rigid, except the thin film on each of the 
surfaces A and B, which are to be put together. Remember 
also that the Royal Institution, in which we are met, has 
been, for the occasion, transported to the centre of the 
earth so that we are not troubled in any way by gravity. 
You see we are not troubled by any trickling down of 
these liquid films—but I must not say down, we have no 
up and down here. You see the liquid film does not 
trickle along these surfaces towards the table, at least you 
must imagine that it does not doso. I now turn one or 
both of these pieces of matter till they are so nearly in 
contact all over the surfaces A and B, that the whole inter- 
| stice becomes filled with water. My metrical sense of touch 
tells me that exactly four and a half centimetre-grammes 
of work has again been done ; this time, however, not by a 
very great force, through a space of less than fifty micro- 
millimetres, but by a very gentle force acting throughout 
the large space of the turning or folding-together motion 
which you have seen, and now see again. We know, in 
fact, by the elementary principle of work done in a 
conservative system, that the work done in the first case 
of letting the two bodies come together directly, and in 
the second case of letting them come together by first 
bringing two points into contact and then folding them 
together, must be the same, and my metrical sense of 
touch has merely told me in this particular sense what we 
all know theoretically must be true in every case of pro- 
ceeding by different ways to the same end from the same 
beginning. WILLIAM THOMSON 
(To be continued.) 
THE TOTAL SOLAR ECLIPSE, 1886 
AUGUST 28-29 
qr Eclipse Expedition will leave England on the 
29th inst. in the Royal Mail Steamship /Vz/e, timed 
to arrive at Barbados on August 11. We regret to learn 
that Her Majesty’s ship Canada, which was told off to 
assist the Expedition, chiefly by supplying artificers and 
assistance in camping and in the observations, has been 
withdrawn on some “diplomatic” service. This is a 
serious blow to the probabilities of good results. 
From data supplied by Mr. Hind, the following details 
have been computed for the Island of Grenada :— 
Latitude Longitude Commencement of totality 
N. W. G.M.T. Local time 
; Aer) hs» §ma- dis. m. Ss. 
Levera 12 13°5 61 37 23 17 19 19 YO 51 
Caliveny... ... I2 0'0 61 43 23907 ATA: Ig I0 22 
Point Saline ... 12 0°5 61 48 23 17 10 19 9 58 
Fort Frederick. 12 3°0 61 44 230 7aI3 19 10 17 
Duration of Sun’s Angle from 
totality Azimuth True altitude N. point 
m. s. nae a 
Levera 3 45 84 12 18 56 87° to W. 
Caliveny ... Ruy 84 6 18 48 GE oy) 
Point Saline 3 48 84 4 18 42 OPE oO 
Fort Frederick . 3 49 84 3 18 46 Chie Se 
The sun’s altitude and azimuth and the angle from 
N. point are given for the commencement of totality. 
The time of first contact for the middle of the island 
{assumed lat. 12° 6"0, long. 61° 430] is 18h. Tim. 55s. 
local mean time at 770 N. to W. on the sun’s limb ; and 
ends at 20h. 20m. 44s. at 105° N. to E. on the limb. 
A diagram is given below showing the position of the 
principal stars and planets at the commencement of 
totality. The distances of the planets from the sun are 
very roughly as follows (the positions of Mercury and 
Venus being shown absolutely, and the directions of the 
others indicated by arrows) :— 
Mercury (Me) = 4 | Mars (Ma) = 15 
Venus (V) — Saturn (S) = 12 
ae } almost in conjunction ee =) 
Local mean time of transit of Polaris and 6 Urse 
Minoris for Caliveny (Grenada), long. 61° 43’ W. :— 
