SCIENCE. 
95 
motion within a solenoid. As soon as the current passes 
it is obliterated by virtue of the attraction, of which Mr. 
Page and Mr. Bourbouze have made such intelligent use. 
The plate, meeting no resistance, turns just as it reaches 
the shoulder. I can give to the spring any tension what- 
ever, so that the time the movable plate takes to make a 
half or quarter revolution can be regulated at will. The 
impression is taken during the passage of the aperture 
in the movable plate across the aperture in the fixed plate. 
It is easily understood how it may be possible to shorten 
the time of passage, either by substituting a simple slit or 
by increasing the tension of the spring. 
In order to estimate the time precisely during which 
an impression is taken, certain experiments are necessary 
which I have not yet been able to carry out, and which 
are of the most delicate kind. I may say that this time 
appears to me not to exceed eight or ten hundredths of a 
second. Should it be found that it is only one half of a 
hundredth, I shall not be at all surprised; for the clear- 
ness with which I have obtained my images proves the 
exposure to be so short, that, when the aerostat is moving 
six to ten metres in a second, it does not traverse any 
perceptible space while the aperture is uncovered. 
A photograph taken at Rouen, in the vertical posi- 
tion, and with by no means favorable circumstances (it 
was after six o’clock in the evening), shows all the objects 
contained in a surface of three hundred metres square. 
I should think that I was then at a distance of noo 
metres from the earth. 
Thanks to the excellent instrument of M. Trouve the 
weight of my apparatus is only 700 grammes, and is so 
manageable that after having made a part of the con- 
nection I have obtained a marvellous view of the Seine, 
showing all of its numerous windings, even to Quilliboeuf, 
and perhaps still farther. — L' Electriciti. 
MR. BRAMWELL ON THE PERKINS SYSTEM. 
In view of the report about to be made by order of the 
United States Government, on what is called the Perkins 
system, employed by the “ Anthracite’’ the little screw 
steam yacht which recently crossed the Atlantic with so 
much success, the following report made by Mr. Bram- 
well at the request of the Perkins Engine Company be- 
fore the departure of the yacht, may be of interest to 
engineers and those interested in steam navigation. 
The engines of the vessel, like her boilers, are of 
peculiar type, and are the invention of Mr. Loftus 
Perkins — of the direct acting inverted pattern with 
surface condensation. They consist of two cylin- 
ders, the after of which is bored in two diameters. 
The smaller diameter bore forms the high pressure 
cylinder, and receives steam from the boiler during the 
first half of the down stroke; the larger diameter is the 
medium or intermediate cylinder, and is supplied at the 
upstroke with the steam used in the smaller bore during 
the preceding downstroke. The exhaust from the large 
bore passes into a chamber, and thence to the low pres- 
sure or forward cjlinder, giving a total expansion of 
thirty-two times. The distribution of steam in the after 
cylinder is effected by three lifting double-beat valves of 
somewhat peculiar construction, but the low pressure or 
forward cylinder is fitted with an ordinary slide-valve, 
having an expansion valve on its back. The condenser 
is fitted with galvanised wrought-iron tubes, rising verii- 
cally from a tube plate, and having closed tops. Within 
these tubes are smaller ones, through which the sea- 
water enters and passes down the annular spaces to the 
inlet of the circulating pump. The exhaust steam comes 
into contact with the exterior of the galvanised tubes, 
and, when condensed, is drawn off and returned to the 
hot well surrounding the upper part of condenser. The 
space between the high-pressure piston and the upper 
side of the intermediate piston is in connection with 
the chamber from which the low-pressure chamber is 
supplied with steam. The cylinders and covers are 
heated by steam, which circulates through wrought-iron 
pipes cast into the thickness of the metal, and they are 
also clothed to prevent loss of heat. The boiler is 
formed of rows of horizontal wrought tubes, 3 inches in 
external diameter, connected at frequent intervals by 
vertical thimbles, the whole series being contained in a 
wrought-iron double casing, having the space filled in 
with vegetable black. The boiler is supplied with fresh 
distilled water, a still being fitted in connection with 
the condenser to keep up the supply. The actual 
dimensions of the cylinders are high pressure inches, 
diameter, intermediate 15 13-16 inches, and the low 
pressure 22 13-16 inches, ihe latter alone being double- 
acting. The stroke is 15 inches. These are the chief 
features of the engines. The trial carried out by Mr. 
Bramwell appears to have been confined to taking 
diagrams, and weighing the coal consumed, which was 
done with minute accuracy, the weight of the sacks 
being deducted from the gross total. But Mr. Bramwell 
says that before comparisons can be properly instituted 
between the economy of the engines of the Anthracite 
and those of different construction, the latter should be 
tried with the same rigor as characterised the trial 
of the former. We venture to think, however, that 
engineers will scarcely regard the trial as a.together what 
could be wished, for there are several questions of 
much interest, to which no answer can be found in the 
report. However, 128 diagrams were taken, and the net 
result shows that the consumption per horse-power was 
i.7lb. per hour, — a very good result for engines so small, 
but not quite so low as might have been expected. The 
precautions taken by Mr. Bramwell to obtain a cor- 
rect estimate were complete so far as they went, and his 
report is minute in its details. The throttle-valve, stop- 
valve, and other parts were sealed in the positions to 
which they were placed, and the coals having been 
weighed into sacks, the bunkers were closed and sealed. 
The trial lasted tor 12 h. 3 min., but after the 15th cwt. of 
coal had been used the engines were allowed to run until 
they stopped through the burning down of the fire. For 
10 hours, however, the mean revolutions were 130.7 per 
minute, the average indicated horse-power during nearly 
nine hours being 80.9. The loss of water during the 
whole 12 hours was 23^ gallons. The mean pressures 
of the various diagrams were ascertained by dividing the 
areas (obtained with the planimeter) by the length of the 
diagrams, a method which Mr. Bramwell thinks more 
accurate than measuring the height. The engines 
worked with remarkable smoothness and regularity, and 
with the exception of tightening up two glands about an 
hour after the start, there was not a spanner or hammer, 
or any tool used about the engines, nor was a single 
handle shifted during the 12 hours the vessel was under 
way. The link motion was in full gear during the whole 
run, with stop-valve full open, and throttle set so as to 
cause the engines to run about 1 30 revolutions per minute. 
About one gallon of lard oil was used, the cylinder and 
slide dispensing with lubricant in the Perkins system; 
grease being inadmissible where it is liable to come into 
contact with the steam in these engines. It is reported 
that the Anthracite , in her voyage across the Atlantic, 
used only 20 tons of coal, and 436 gallons of fresh water, 
and it would be of considerable interest, as Mr. Bramwell 
suggests, to have a thorough trial of a compound engine 
of about the same power, viz., from 70 to 90 horse-power. 
In connection with the trial upon which Mr. Bramwell re- 
ports there is a point which we should like to see elucidated. 
The boiler-pressure is supposed to have been somewhere 
about 3601b. on the square inch, but the maximum pres- 
sure on the first piston is only about 2oolb., and the aver- 
age in the first cylinder about izolb., a rather serious 
discrepancy, though this ratio of loss is not unknown. 
— Eng. Mech. 
