SCIENTIFIC SUMMARY, 
111 
speaking, forms a store of available force that may afterwards be recovered. 
(2) There is the period during which the magnet is pulling its keeper to 
itself, and is positively doing actual work. Now, paradoxical as it may 
seem, it is a fact that during this period (No. 2), while the magnet is doing 
actual work, the intensity and the consumption of zinc is actually dimi- 
nished, so that, in one sense, the more work done the less the fuel (so to 
speak) which is consumed in doing it. It is in this point that a galvanic 
battery differs from other machines which do work. It is as if a horse, 
when he did work, ate actually less food than when he was idle, and wasted 
less muscle, or as if a locomotive consumed less fuel when in motion than 
when at rest. (3) Then comes the third period, when the keeper has been 
pulled home, and the weight is merely sustained. During this period no 
actual work is being done, and the weight sustained only shows what work 
the magnet is capable of doing, and so serves as a measure of its potentiality, 
and during this period (No. 3), strange to say, more zinc is consumed per 
unit of time than while the work is being done. In practice, therefore, in 
an electro-dynamic engine, period 3 should be reduced to nil. Now break 
the circuit. If there be a secondary wire (as in a Ruhmkorff coil) the 
tension produced during the first period may be utilised in some way by the 
counter current produced in thus breaking the circuit, and the same series of 
phenomena may then begin over again. 
The Films of Liquids, and Cohesion Figures . — In connection with this 
matter, Mr. Charles Tomlinson, F.R.S., has been making some interesting 
experiments. Under date Nov. 28, he w r rites an account of the following 
experiments to the u Chemical News ” : — A very strong solution of sodic 
sulphate was boiled in a large flask and then filtered into six small flasks, 
each of which was again boiled and set aside to cool, covered with a 
watchglass. Some oil of citronella, diluted with two or three times 
its volume of ether, was taken up in a straight dropping-tube furnished 
with an india-rubber shield, as described in my mode of testing M. Jeannel’s 
experiment (see u Chemical News,” vol. xxi. p. 52). The watchglass 
was gently removed from the flask No. 1, and the dropping-tube inserted ; 
after some minutes a drop fell from the tube, the ether in spreading over the 
surface described its cohesion figure, and the solution crystallised imme- 
diately. In Nos. 2 . to 5 the dropping-tube was lowered so as to deliver the 
drop very gently, or it was allowed to trickle down the side of the flask. In 
two cases the ether evaporated and left the oil on the surface in minute 
lenses ; there was no crystallisation even on gently shaking the solution. In 
No. 4 a film was formed on the side of the flask ; on inclining it so as to 
bring the solution into contact with it, crystallisation set in. In No. 6 a 
film was formed on the surface, but on gently shaking the flask the solution 
became solid. 
Bust in the Air . — At the British Association Mr. C. R. Titchborne gives 
an account of his later experiments on the Dublin atmosphere. His obser- 
vations, so far as they go, seem to point to a curious phase of the subject — 
that is, that dust taken at a great height, and in such a position as in certain 
experiments, should appear to have as great, or greater activity, than that 
which would be obtained from a building which is nightly crowded to suffo- 
cation. This, in some measure, may be due to the extreme levity of the 
