1849.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



93 



scribed at the previous meeting, the author proceeded with his investigations 

 of the remaining part of the suhject. 



The action of the Galvanic Battery was first treated of, and the peouhari- 

 ties attending this mode of producing electrical power were investigated. 

 Two specimens of common green glass cells were exhibited, and the peculiar 

 effects produced by arranging a series of galvanic batteries in various order 

 were noticed ; and an arrangement of galvanic batteries, producing what the 

 author called the Electrical Paradox, was exhibited. In this arrangement it 

 was shown how that the power from a galvanic battery, however large the 

 area of the plates of that battery were, might be entirely stopped, or the 

 current even reversed, by another battery so small that it would pass through 

 the eye of a needle. The application of this principle, and the effects that 

 would thereby be produced on certain arrangements of electric telegraphs, 

 were briefly stated. The author then alluded to the rapid oxidation of the 

 iron railings in the squares of London, and showed how that the effect was 

 due to a galvanization arising from the use of lead for connecting the iron 

 with the stone walls. 



The author then exhibited the Gold Leaf Telegraph, and remarked on the 

 very small amount of resistance offered to the electric current by this ar- 

 rangement. This telegraph was then exhibited at work by electricity de- 

 veloped from a burning taper. It was observed that the Gold Leaf Tele- 

 graph was selected by the commissioners appointed by the government of 

 Baden to report on the kind of telegraph best suited for the use of that go- 

 vernment, and that its practical use in Germany during the last year-and-a- 

 half had given every satisfaction. 



The next subject treated of was the Conducting JVires, Here the author 

 remarked on the laws of the transmission of the electrical power over the 

 wires, and showed how the peculiarities attendant on the use of electricity 

 in connection with line wires for telegraphic purposes might he most advan- 

 tageously employed. — Various modes of insulation in use were also noticed. 



The author then alluded to the action of natural displays of the electrical 

 power in the form of Lighlning and the Aurora Borealis. Specimens of 

 parts of telegraphic instruments, burnt and melted by the action of light- 

 ning, were exhibited. A description was also given of the effects observed 

 on the telegraph wires in the Kilsby Tunnel, on the London and North- 

 Western Railway, during a violent thunderstorm in 1848. Various modes of 

 counteracting the effects of lightning on electric telegraphs were investi- 

 gated, and new plans for preventing damage or danger therefrom were sug- 

 gested. The author then described a very remarkable eflfect produced on 

 the telegraphic instrument on the London and North-Western Railway, on 

 the 24th September, 1847, and said the cause of such effects was as yet en- 

 veloped in mystery. The manner in which the electric telegraphs were af- 

 fected during the beautiful auroreal display of the 17th of November, 1848, 

 weie minutely described, and the action upon the wires where the greater 

 portion of their length was in the inside of a tunnel, was noticed. 



Various experiments were made by the author during the evening; the 

 paper was illustrated by numerous diagrams ; and a series of new electric 

 telegraphs were exhibited at work. 



Jan. 31.— W. TooKE, Esq., F.R.S., in the Chair. 



Robert Hunt, Esq., read a paper " On the Photographometer,for mea- 

 suring the intensity of the Chemical Action of the rays of Light on all Pho- 

 tographic preparations, and for affording a means of comparing the Sensi- 

 tiveness of the same" By A. Claudet, Esq. 



The art of photography, observes the author, is founded on the property 

 with which light is endowed — namely, of producing a photographic effect 

 when it strikes upon certain clieiuical coujpounds. The effect being in pro- 

 portion to the intensity of the light during a given space of time, it is 

 necessary, for the success of the operation, to be able to ascertain the exact 

 power of the light at any particular moment, and the only means of so doing 

 hitherto possessed by the photographer, is the effect it produces on the eye. 

 A few only of the rays which emanate from the sun are capable of producing 

 on the chemically-prepared surface, an effect which is the cause of the pho- 

 tographic picture; and if it were possible to admit into a room only the rays 

 which are endowed with the power of affecting the photogenic preparation, 

 the objects in the room would not be visible to the eye, as the room would 

 appear to be plunged in darkness, while the objects in it would reflect some 

 invisible rays which are capable of producing the photographic image. — This 

 fact the author illustrated by a series of specimens, in which the effects of 

 rays of light were reflected from the various colours used on porcelain. 



The property of absorption possessed by red, orange, yellow, and green 

 glass being known to photographers, and the power of admitting thmugh 

 blue glass nearly all the photogenic rays which are not luminous, combined 

 with the improvements which have taken place since the discovery of the 

 art by Daugerre, enable the photographist of the present time to employ a 

 very soft light, and to place the sitter in the shade. 



The action of the blue and yellow rays was shown by covering a large 

 print, one half with dark blue, and the other half with yellow glass. That 

 portion of the print which was visible to the eye through yellow glass, was 

 rendered invisible by the action of the ray on the photographic plate ; while 

 the ray reflected from the blue glass, which entirely obscured the picture, 

 was rendered perfectly clear and distinct. — Several specimens, intended to 

 show that theluminous and photogenic rays are not the same, were also ex- 

 hibited. 



Several philosophers are of opinion that the photogenic rays are as inde- 

 pendent of the light as heat is, although they are sent forth from the same 



source, and travel together at the same velocity, and are subject to the same 

 laws of reflection, refraction, and polarization. The actinic or photogenic 

 rays are situated at the most refrangible part of the prismatic spectrum, and 

 are thus refracted to the same degree as the blue, indigo, or violet rays. A 

 series of experiments on various colours obtained by artificial means were 

 next exhibited, the whole tending to prove that the atmosphere of London 

 with its smoke and fog, is too often for the photographer like the ray from 

 the yellow glass. 



As the result of the photographic operation depends on the intensity of 

 the actinic rays, and also upon the degree of the sentiveness of the chernical 

 preparation, M. Claudet has constructed an apparatus which is not only 

 capable of measuring the photogenic light, but of testing the sensitiveness of 

 the chemical preparation of the Daugerreotype plate. This instrument is 

 constructed so that a plate being placed upon an inclined plane, will always 

 fall with the same rapidity. For each operation, the plate has seven vertical 

 slits or openings cut in if ; these are placed parallel to each other, the first 

 being 1 mdlimetre wide ; the second, 2; the third, 4; the fourth, 8; the fifth, 

 16; the sixth, 32; and the seventh, 04 millimetres. The photographic sur- 

 face is placed at nearly the bottom of the iticlined plane, under a metallic 

 plate, pierced with seven circular holes, corresponding with the openings of 

 the moveable plate containing the proportionate apertures. When the move- 

 able plate passes before the photogenic surface covered with the seven circu- 

 lar holes, the light strikes upon the spaces left open by the circular holes, in 

 various intensities. The space lighted by the opening of 64 millimetres will 

 be aftected by an intensity double that which is lighted by 32 millimetres ; 

 quadruple that of the next under the opening of 16 millimetres ; and so on, 

 until the last opening, which being only 1 millimetre, will have received 04 

 times less light than the first ; so that after the operation seven round figures, 

 or less, according to the intensity of the light, are represented upon the pho- 

 tographic plate. The photographer is thus enabled to ascertain how long it 

 will be necessary to submit the plate to the action of the light on the camera 

 by the length of time required to dcvelope the seven round figures. Let us 

 suppose that he waits ten seconds, and he finds only six instead of seven of 

 the round figures, it would prove that the light is one-half less intense than 

 he required, so that he must wait 20 seconds instead of 10 ; if only five, 

 40 seconds; if four, 80 seconds; if three, 160 seconds ;if two, 320 seconds ; 

 if one, 640 secouds. This is quite sufficient for general purposes of photo- 

 graphy ; but for scientific investigations, M. Claudet has continued the geo- 

 njctrical progression, and instead of from 1 to 6, he has continued the pro- 

 gression from 1 to 8192. This is pfl'ected by having two plates and four 

 series of holes in each plate, and shutting one series after every fall of the 

 moveable plate. By repeating the falls, the intensity is doubled, trebled, 

 quadrupled, and so on ; and after the operation each plate represents four 

 series of round figures, showing the various eft'ects of all the intensities, from 

 1 to 8192. 



M. Claudet's Photographometer enables the operator to compare the sen- 

 sitiveness of two difterent preparations, so that the photographer can con- 

 stantly bji experiments improve the sensitiveness of the surface. 



Mr. T. B. Jordan gave a short account of Mr. Cochran's machine for saw- 

 ing timbers with curved and bevelled faces, and a working model was exhi- 

 bited to the meeting. 



INSTITUTION OF CIVIL ENGINEERS. 



Feb. 6. — J. Field, Esq., President, in the Chair. 



The paper read was a " Description of the Ablattoirs of Paris.' By 

 Mr. 11 B. Grantham, IVI. Inst. CE. 



The subject treated of was chiefly in connection with the sanitary ques- 

 tion, at present occupying so much attention ; the author being of opinion 

 that much public benefit would be derived from the introduction of similar 

 establishments into the city of Lotdon. The paper commenced by point- 

 ing out the advantages resulting from the method iu which the butchers' 

 trade was carried ou in Paris. It was stated that this trade was regu- 

 lated by a number of restrictive enactments, and conducted under the 

 control of a syndicate or guild, who advised with the government upon all 

 questions relating to the abbattoirsand markets. 



It appeared from the account that, previous to the opening of the abat- 

 toirs, in 1818, slaughter-houses existed in the crowded and populous dis- 

 tricts of the city ; and that (as at present in Loudon), the passage of the 

 cattle through the streets, and the consequent nuisauces, were found to be 

 intolerable. The five abbattoirs were designed with great care, to cbviiile 

 these evils, and were generally allowed to have fully accomplished the 

 purposes for which they had been constructed ; they had been of great 

 public service, in rendering Paris free from those nuisances whiih were 

 still permitted to exist as such blots on the general cleanliness of the city 

 of Loiidon. The abbattoirs were erected within the Barriers, opposite 

 Montnuirtre, Menil-Moutaut, Greuelle, Du Roule, and Ville Juif, at an 

 average distance of a mile and three quarters from the centre of the city. 



The paper, which was accompauied by detailed plans of each abbattoir, 

 and a general drawing of their arrangement, described minutely their con- 

 struction, as well as the mode of slaughtering the cattle, the melting the 

 tallow, and other details connected with the trade carried ou therein. All 

 the buildings were stated to be abundantly supplied with water, will 

 ventilated, and kept in the highest stale of cleanllne^s. 



