38G 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[NOVKMBKR, 



16 pints of distilled water; it is then subjected to the heat of charcoal or a 

 spirit lamp until a firm white coating is formed all over the surface of the 

 «Uver. The plate is then suddenly cooled. This process is repeated three 

 times] It is placed in a dark chamber with the face or silver surface down- 

 wards, where it is acted upon by the spontaneous evaporation of iodine ; this 

 condenses upon the silver, and produces a fine gold-coloured surface, ex- 

 tremely sensitive to the impressions of light. It is then placed in a camera 

 obscura, the light having becu until then perfectly excluded from it. It there 

 receives the impression of any images brought within the focal plane ; and 

 by subsequently e.vposing il in a dark, close chamber, with its silver surface 

 downwards, to'the fumes of heated mercury, the images are rendered visible ; 

 to fix the images so received, the iodine is removed by dipping the plate in 

 pure water, and then washing it either with a weak solution of hypo-sulphite 

 of soda or a saturated solution of common salt, and finally dipping it in dis- 

 tilled water and drying it. It should then be framed and glazed to preserve 

 it from external injury, and the picture will remain unchanged. 



Attempts have been made to use this process for preparing the plates for 

 engravers, as much time and cost would thereby be saved, but hitherto it has 

 not been done to any extent. 



The author presses upon the Institution the applicability of these processes 

 to engineering uses, and quotes the remark of "Mons. .\rago — " That photo- 

 graphic delineations having Ijcen subjected during their formation to the 

 rules of geometry, we may be enabled, by the aid of a few simple data, to 

 ascertain the exact dimensions of tin- most elevated parts of the most inac- 

 cessible edifices." 



Mr. Cooper, Senior, introduced the subject of photography by explaining, 

 and illustrating by instruments and diagrams, the principles of the division 

 and dispersion of the rays of light, according to the Newtonian theory, as 

 well as the most recent researches into the subject. He described the 

 chemical properties of light — its affinity for certain combinations, such as 

 chloride of silver — its heating powers — the different effects of the rays on 

 vegetation — and the application of these known principles to photography. 

 He then explained the chemical properties of the chloride of silver, iodine, 

 and other substances used in the process. In alluding to the probable uses 

 of the Daguerreotype, he observed that the process might be employed to 

 make drawings of machinery, as graduated scales might be fixed to certain 

 parts of the objects, and they would be copied in their relative proportions 

 to the machine. 



Jlr. Cooper, Junior, illustrated Mr. Gordon's communication by explaining 

 the photographic apparatus, and the process of obtaining a specimen of 

 Daguerreotype by means of the oxy-hydrogen light. He described, among 

 other points, the difficulty of obtaining pure silver upon the copper plates, 

 as, for the advantage in rolling, the manufacturer will introduce an alloy 

 of J to 1 5 per cent. On this account, acid is used so repeatedly in cleaning 

 the plates, that any particles of copper which have been rolled into the 

 surface may be carried off. He explained his improveiucnt to the iodine 

 box, which consists in spreading the iodine all over the bottom of a tray 

 lined with glass, and covering it with a piece of card-board, wliich becomes 

 saturated with the fumes of the iodine, and on the silvered plate being placed 

 over it, acts equally over its surface, instead of partially, as in the old system 

 of placing the iodine in a mass in the centre of the tray. He had found this 

 to be a great improvement. The shortest time in which he bad obtained a 

 photographic picture in England was 11 minutes; while, during a gloomy 

 day in November, it took an hour and a half to procure a moderately good 

 one. 



" An Universal Screu'-Jack." By George England. 



This machine, a model of which was presented to the Institution, is in- 

 tended for raising heav7 weights and moving them in any required direction ; 

 the vertical motion is similar to that of a common screw-Ufting jack, and the 

 lateral motion is communicated by a ratchet lever to a horizontal screw, 

 working in bearings on a strong cast-iron bed with planed surfaces through a 

 double nut attached to the base of the jack. The jack has been found useful 

 for erecting heavy pieces of machinery, and for replacing railway carriages 

 and locomotives on the rails when they have been accidentally thrown off. 

 " Description of a Traversiny Screw-Jack." By W. J. Curtis. 

 The screw-jack is attached to a plank w^itb a rack in it, and slides in a 

 groove in another plank which is placed beneath it, across the railway ; in 

 the lower plank is a rack, by means of which and a hooked lever, tlie jack, 

 with the engine or any other weight resting upon it, is drawn easily across 

 the rails and lowered to its proper position. By this apparatus, engines and 

 carriages of considerable weight have been replaced on a railway by two men 

 in a very short space of time. 



A model of the machine was presented to the Institution. 



May 19. — The President in the Chair. 



Peter Bruff was balloted for aud elected an Associate. 



'• Description of a new Gas Reyula/or." By James Milne. 



The object of this instrument (which tlie inventor exhibited in action, and 

 presented to the Institution) is to regulate the supply of gas to burners, so 

 that any variation in the pressure, arising from extinguishing the adjacent 

 hghts along the line of the street main, or in the diflferent floors of manu- 

 factories, shall not affect those lights which are supplied through the regu- 

 lator. 



The regulator consists of a cylindrical outer case, to which is affixed a 

 water gauge to show the pressure ; to the top is attached an inner cylinder, 

 open at the lower end and reaching nearly to the bottom of llie outer case; 

 tlie gas is introduced from beneath by a tube in the centre, terminating in a 

 conical valve at the top ; the male part of the valve is fixed by three arms to 

 the top of a float, which moves freely in the space l)etween the inner cylinder 

 and the centre tulie ; the areas between the outer case and the inner cylinder, 

 ami between the inner cylinder and the centre tube, being alike, the pressure 

 of the gas acts upon the water within the inner cylinder, and causes it to 

 rise in the outer case just as much as it is depressed in the inner space. This 

 depression carries down the float with the male part of the valve attached 

 to it, and thus diminishes the aperture of the supply pipe, until the pressure 

 is relieved by other burners being lighted, and enables the supply of gas to 

 be in proportion to the demand. The pressure may be regulated at will by 

 increasing or diminishing tlie quantity of v, ater in the cylinders, and it is 

 shown correctly by the graduated glass [range. This apparatus has been 

 found, in an experience of two years, to effect a saving of about 20 per cent., 

 independent of its ensuring a perfect equality to all the burners in action. 

 Drawings of the instrument accompanied this communication. 



Mr Lowe believed the " gas regulator" to be an efficient instrument. It 

 was of the utmost importance that the light from gas should he steady aud 

 equal, as the nerves of the eye were more injured by an unsteady than by an 

 intense light. In large estabhshraents, the greatest care would scarcely pre- 

 vent constant variation in the lights, so that an efficient means of producing 

 regularity must be valuable. 



BRITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. 



Tenth Meeting. — September, 1840. 



(From the Atheneeum.J 



Section G. — Mechanic.\l Science. 



Mr. Dircks gave an account of a railway irheet with wood tyre, which was 

 exhiliited in the museum. It was one of a set which had been in use for two 

 months, carrying five tons each day. The construction of the wheel will be 

 understood by imagining an ordinary spoked wheel, but with a deep-eAa»»- 

 nelled tyre. In this channel is inserted blocks of African oak, measuring 

 about 4 X 3i inches, prepared by filling the pores with such unctions prepa- 

 rations as counteract the effects of capillary attraction in regard to wet or 

 damp. The blocks are cut so as to fit very exactly, with the grain placed 

 vertically throughout, forming a kind of wooden tyre. There are about thirty 

 blocks of wood round each wheel, where they are retained in their places by 

 bolts, the two sides of the channel having corresponding holes drilled through 

 them for this purpose ; each block of wood is thus fastened by one or two 

 bolts, which are afterwards well rivetted. After being so fitted, the wheel is 

 put into a lathe, and fumed in the ordinary manner of turning iron tyres, 

 when it acquires all the appearance of a common railway wheel, but with an 

 outer wooden rim, and the flange only of iron. Mr. Du'cks proposes the use 

 of either hard or soft woods, and of various chemical preparations to prevent 

 the admission of water into the pores of the wood : he also contemplates the 

 using of wood well compressed. 



Mr. JeftVey on a New Hydraulic Jppnralm. — It comprised an improvement 

 on the ancient endless chain of buckets, which he considers of Egyptian origin. 

 This apparatus has hitherto never acquired the value it admits of, on account 

 of a defect having remained in its construction, opposed to geometrical prin- 

 ciple — the buckets which bring up the water being fixed outside instead of 

 within the rope. The effect of this is such an acceleration of the bucket, 

 when it is carried round the wheel at top, as causes it to overtake the water 

 and carry much of it down again. But, liy placing the buckets on the centre 

 side of the ropes, that is, within them, the bucket when passing round the 

 wheel, being very near the centre, is much retarded, and the momentum of 

 the water causes it to ride out of the bucket very effectually into the trough. 

 A peculiarity in the form of the bucket also prevents the spilling of the water 

 in cases where the motion is very slow. 



Sir J. Robison stated that, although the methods in India are rude, yet 

 they give a greater return of work done for power applied than other methods 

 known. — Mr. Jeffrey stated that he bad tried this method on a large scale, 

 each bucket containing IJ cwt. of water. A small valve at the liottom of the 

 bucket allows the air to enter, aud the bucket is thus quickly emptied. 



" Additional Notice conceminy the most economical and effective proportion 

 of Engine Power to the tonnaye of the hull in Steam Vessels, and more espe- 

 cially in those desiyned for long voyages." By Mr. Scott Russell 



Lai-gc power or small power ? has always been a disputed question. The 

 early steam boat engines had but a small power proportioned to the tonnage. 

 The Comet had 25 tons burden, and only three horses power— being a pro- 

 portion of power to tonnage amounting to i- On this subject modern prac- 

 tice and opinion seem to offer no guide. The East India Company have used 

 low proportions of power to tonnage, and in this they appear to have adopted 

 the general ma.\ims of Southern engineers. The Government appear also to 

 have followed the same course, but without going to the same extreme. The 

 Clyde engineers adopt the opposite maxim, and place as much power in their 

 vessels as can be conveniently applied. There appears at present to be a 



