294 
NATURE 
[Fuly 29, 1886. 
lution. This line is vertical in the realisation now to be 
given, and it or any line parallel to it will be called vertical 
in the drawing, and any line perpendicular to it will be 
called horizontal. The distance between any two hori- 
zontal lines in the drawing will be called dference of 
levels. 
Through any point, N, of the axis draw a line, N P, cutting 
it at any angle. With any point, 0, as centre on the line 
NP, describe a very small circular arc through P P’, and let 
N’ be the point in which the line of 0 P’ cuts the axis. 
Measure N P, N’ P’, and the difference of levels between P | L : J 
result of his labours was a series of skilfully executed 
and Pp’. Denoting this last by 6, and taking @ as a linear 
parameter, calculate the value of 
fo I I I ye 
(2 top tue we | 
Take this length on the compasses, and putting the 
pencil point at P’, place the other point at 0’ on the line P’N’, 
and with 0’ as centre, describe a small arc, P’ P". Con- 
tinue the process according to the same rule, and the 
successive very small arcs so drawn will constitute a 
curved line, which is the generating line of the surface of 
revolution inclosing the liquid, according to the conditions 
of the special case treated. 
This method of solving the capillary equation for sur- 
faces of revolution remained unused for fifteen or twenty 
years, until in 1874 I placed it in the hands of Mr. John 
Perry (now Professor of Mechanics at the City and Guilds 
Institute), who was then attending the Natural Philosophy 
Laboratory of Glasgow University. He worked out the 
problem with great perseverance and ability, and the 
drawings representing a large variety of cases of the 
capillary surfaces of revolution. These drawings, which 
are most instructive and valuable, I have not yet been 
able to prepare for publication, but the most characteristic 
of them have been reproduced on an enlarged scale, and 
are now on the screen before you.! Three of the diagrams, 
those to which I am now pointing (Figs. 10, 11, and 12), 
illustrate strictly theoretical solutions—that is to say, the 
curves there shown do not represent real capillary sur- 
AXIS OF -Z 
faces—but these mathematical extensions of the problem, 
while most interesting and instructive, are such as cannot 
be adequately:treated in the tinie now at my disposal. 
WILLIAM THOMSON 
(To be continued.) 
THE SCIENCE AND ART DEPARTMENT 
EXAMINATION IN CHEMISTRY 
HE new editor of the “Science and Art Directory” 
announces a new departure of the most important 
kind in the teaching of chemistry. In addition to the 
oral instruction in the elementary stage, there is now 
introduced an alternative first stage or elementary course 
intended {or those students who only require the elements 
of chemistr;; as a foundation for their studies in other 
subjects. 
We give the new syllabus so that it may speak for it- 
self, and congratulate the Department on a step in 
| Crystallisation. 
spring, river, and pond waters, &c. 
G. 12. 
harmony with the views of the best friends of scientific 
education in this country. 
SoLuTION.—Disappearance of a solid in a liquid by solution. 
Saturation of a liquid. Effect of increase of temperature on 
saturation. Effect of lowering the temperature on saturation. 
Filtration. Solvent properties of water. Rain, 
Solid matter in different 
waters ; how estimated. Loch Katrine water. Thames water. 
Sea water. Hard and soft waters. Mineral waters. Similar 
solvent of other liquids. Solution of one liquid in another. 
Liquids insoluble in one another. Solution of gases in water 
and other liquids. The effect of heat on the quantity of gas 
dissolved by a liquid. : A 
Experimen(s.—Suspend a piece of white sugar by a thread in 
a glass vessel containing water. Dissolve salt in water. Show 
on a balance that sugar or salt and water when separate and 
when dissolved weigh the same. Show that salt is obtained 
* The diagrams here referred to are now published in Figs. ro to 24 of the 
present report of the lecture at the Royal Institution. ‘These figures are 
accurate copies of Mr. Perry’s original drawings, and J desire to acknow- 
ledge the great care and attention which Mr. Cooper, engraver to NATURE, 
has given to the work. 
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