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 Iioo 

 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' Electricity. 



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 tne 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 cylinder, 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 verti- 

 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 heal. 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 J% inches, 

 diameter, intermediate 15 13-16 inches, and the low 

 pressure 22 13-16 inches, the 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 altogether 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 

 1.71b. 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 for 12 h. 3min., 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 130 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 360IS. 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 i2olb., a rather serious 

 discrepancy, though this ratio of loss is not unknown. 

 — Eng. Mech. 



