ELECTRICITY. 



273 



axis. Immediately in front of tlio edge of 

 eaoh disk is placed tho terminal of an olectrio 

 other end of which is connected 

 :i gun, |H-rhaps fifty or one hundred yards 

 it. Through tho sides of tho gun, nt 

 i- distances from breech to muzzle, iron 

 arc screwed. In tho centre of each 

 phi:: works a piston, which by pressure against 

 uer end can bo pushed slightly outwiml ; 

 outer end tho wire is attached. When 

 all is ready, tho disks of the chronoscopo are 

 made to rotate by the wheel- work with great 

 velocity; the gun is fired; the projectile, as it 

 ni-iln's along the bore, pushes the inner ends 

 of the pistons one after the othor; the outer 

 ends give a slight jump, sufficient, however, 

 to cut the wires thereto attached, and by this 

 cutting a spark is on the instant produced at 

 the terminal on the chronoscope. The edges 

 of tho disk havo previously been coated with 

 white paper under a film of lampblack ; the 

 spark burns otf a minute speck of the black, 

 leaving, of course, a speck of the white paper 

 visible beneath. The first spark comes from 

 the wire nearest the breech, the last from the 

 one nearest the muzzle, and the intermediate 

 ones in their order. The time between one 

 and the other is almost inconceivably small, 

 but, as the chronoscope will measure the 

 hundred-thousandth part of a second, the 

 movement of the projectile along the gun is ac- 

 curately recorded by the sparks on the disks, 

 and is read off on a scale to four or five places 

 of decimals. 



Electric Buoy. During the early part of the 

 year an electric buoy, the invention of M. E. 

 Duchemin, was exhibited at Cherbourg by or- 

 der of the French Minister of Marine. The 

 electricity was produced by the constantly- 

 renewed action of sea-water on zinc, but the 

 inventor has since demonstrated that an in- 

 crease of intensity could be obtained by means 

 of certain chemical agents held in suspension 

 around the zinc, or the charcoal element. The 

 new battery resulting from the experiments 

 consists of a porous vase fixed on a wooden 

 buoy or floater. The vase is surrounded by a 

 thick zinc cylinder, pierced with holes, the 

 wire of which represents the negative pole. 

 Within the porous vase is placed a slab of gas- 

 retort charcoal, to which is affixed tho con- 

 ductor of the positive pole ; the charcoal is 

 surrounded by pieces of coke and perchlorato 

 of iron. The vase is carefully closed, and tho 

 battery, when plunged in tho sea, immediately 

 gives forth large quantities of electricity. 



Electrical Resistance Pyrometer. Nature 

 says of this invention by Mr. 0. W. Siemens, 

 that it is the very salamander of pyrometers, 

 and will measure the temperature of tho most 

 highly-heated furnace, which must render it 

 indispensable in operations where intense heat 

 is required, and to all experimentalists who 

 know the imperfections of tho pyrometer in 

 ordinary use. The construction of the new 

 instrument is based on the physical fact that 

 VOL. x. 18 A 



tho resistance of pure metals to tho electric 

 current increases with increase of temperature 

 in a simple absolute ratio. A platinum wire 

 of known resistance is coiled upon a small cyl- 

 inil. r of tiro-clay, and is covered by a tube of 

 the same metal, which protects the wire from 

 the destructive action of flame, without pre- 

 venting access of heat. Thus constructed, the 

 pyrometer is placed in the furnace, and is con- 

 nected by wires with a DaniclPs battery of two 

 cells, and with a compact resistance-measnrer, 

 specially devised by Mr. Siemens, on which 

 the observer makes observations at his ease. 

 As the fire burns, the electrical resistance of 

 the platinum coil rapidly increases, and commu- 

 nicates its progress to the measurer, on which 

 tho indications of temperature may be read off 

 as entirely trustworthy, even up to the melting- 

 point of platinum. 



Electro-magnetic Anemometer. This inven- 

 tion, by Mr. J. J. Hall, for registering the ve- 

 locity and pressure of the wind, is composed 

 of two parts, one for each of these purposes. 

 The velocity apparatus consists of a set of 

 Robinson's hemispherical cups, which commu- 

 nicate their motion downward into a brass box, 

 where it is reduced in angular velocity, and 

 causes a contact disk or commutator (in which 

 two platinum contact pins are fixed equidistant 

 from one another) to revolve in -j^th mile. An 

 insulated metallic lever, having a platinum 

 working face, stands on either side of the disk, 

 so that upon the completion of every yj^th 

 mile one or other of the contact pins comes in 

 contact with the two lovers, thus uniting them 

 and completing the circuit. The levers are 

 raised a few degrees, and then fall back to 

 their normal position ready to be taken up by 

 the next pin, and so on. The recording appa- 

 ratus consists of a train of wheels and pinions 

 working in a frame or between two brass 

 plates, tho arbors of which project through a 

 dial-plate whereon the circles and figures are 

 engraved and carry the hands. These wheels 

 are driven by a weight attached to a line 

 wound round a barrel, and a locking-pin disk 

 (the pinion of which works in the first wheel) 

 is released, at every contact of the cup-appara- 

 tus, by an electro-magnet, which unlocks the 

 pin-disk and allows tho first hand to advance 

 TpJ^th mile on the graduated dial, by a jump 

 similar to the minute-hands in remontoire 

 clocks. By turning on a " strike-silent " stop 

 a hammer lever is brought into connection 

 with the escapement and strikes a bell at every 

 contact. By this arrangement the observer 

 has nothing to do but to notice tho seconds- 

 hand of his watch or chronometer while he 

 counts tho number of times that the bell is 

 struck, each of which corresponds to the five- 

 hundredth part of a mile, and by a formula 

 arranged by Mr. Hall (who has also arranged 

 a comprehensive series of tables for use with 

 this instrument) the hourly velocity may be 

 readily deduced. In noting velocities extend- 

 ing over long periods of time, the instrument 



