1839.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



151 



:e 



oxidizing power of tlio chemical rays in their action on recentlyiireciiiilated 

 chloride of silver ; secondl}', the instant and copious precipitation of a mix- 

 ture of a solution of muriate of platina and lime-water, by solar light, 

 forming an insoluble compound, which might afterwards bo blackened by 

 a variety of agents : thirdly, the reduction of gold in contact with de- 

 oxidizing agents : and fourthly, the decomposition of an argentine compound, 

 soluble in water exposed to light, in an atmosphere of peroxide of chlorine, 

 either piu'c or diluted. Confining his attention, in tho present notice, to the 

 employment of chloride of silver, the author inquires into the methods by 

 which the blackened traces can be preserved ; which may be effected, he 

 observes, by the application of any liquid capable of dissolving and washing 

 off the unchanged chloride, but of leaving the reduced, or oxide ol silver, 

 untouched. These conditions are best fulfilled by the liquid hyjiosulphites. 

 Pure water will fix tho photograph, by washing out the nitrate of silver, but 

 the tint of the picture resulting is brick-red ; but the black colour may be 

 restored, by washing it over with a weak solution of hyposulphite of aai- 

 monia. The author found that paper impregnated with the chloride of 

 silver was only shglitly susceptible to the influence of light; but an acci- 

 dental observation led him to the discovery of other salts of silver, in which 

 the acid, being more volatile, adheres to the base by a weak affinity, and 

 which impart much greater sensibility to the paper on which they are ap- 

 plied — such as the carbonate the nitrate, and the acetate. The nitrate re- 

 quires to be perfectly neutral ; for the least excess of acid lowers, in a re- 

 markable degree, its susceptibility. In the application of iihotographic pro- 

 cesses to the copying of engravings or diawings, many precautions, and 

 minute attention to a number of apparently trivial, but really important 

 circumstances, are required to insure success. In the first transfers, both 

 light and shadow, as well as right and left, are the reverse of the oiiginal ; 

 and to operate a second transfer, or by a double inversion tt» reproduce the 

 original effect, is a matter of infinitely greater difficulty, and in which the 

 author has only recently ascertained the cause of former failures, and the 

 remedy to be applied. It was during the prosecution that these ex|ierimenls 

 that the author was led to notice some remarkable facts relating to the 

 action of tho chemical rays. He ascertained the contrary to the prevailing 

 opinion : the chemical action of light is by no means proportional to the 

 quantity of violet rays transmitted, or even to the general tendency of the 

 tint to the violet end of the spectrum ; and his experiments lead to the con- 

 clusion, that, in the same manner as media have been ascertained to have 

 relations 5H' tjeneris to the calorific rays, uot regulated by their relations 

 to the rays of illumination and of colour, they have also specific relatioes to 

 the chemical spectrum, diff'erent from those they bear to the other kinds of 

 spectra. For the successful prosecution of this curious investigation, the 

 firfct step must consist in the minute e.xamination of the chemical 

 actions of all the parts of a pure spectrum, not formed by material prisms, 

 and he points out, for that purpose, one formed in Fraueuhoier's method, by 

 the interference of the rays of light themselves in passing through gratings, 

 and fixed by the heliostat. He notices a curious phenomenon respecting 

 the action of light on nitrated paper; namely, its great increase of intensity 

 under a certain kind of glass strongly pressed in contact with it — an effect 

 which cannot be explained either by the reflection of light or the presence 

 of moisture, but which may possibly be dependent on the evolution of heal. 

 Twenty-three specimens of photographs made by Sir .lolin Herschel ac- 

 company this paper; one a sketch of liis telescope at Slough, fixed from 

 its image in a lens, and the rest copies of engravings and drawings, some 

 reverse, or first transfers, and others second trauefers, or re-reversed pic- 

 tures. 



GEOLOGICAL SOCIETY. 



Feb. 27. — The Rev. Dr. Blckland, President, in the Chair. 



The tbUovving communications were read : — 



1. " On Jmprctisiuns of Drojis of Rain un Slabs of New Red Sand'itoiie, 

 in the Storcton Qiinrries, Cheshire, and coeval with Hie formation of the 

 Strata," Itij Mr. John Cunninyham, of Liverpool. — In a paper read belore 

 the Society on the .3rd of December, an account was given of the impres- 

 sions of footsteps of several species of animals in tlie new red sandstone of 

 the Storcton Quarries, about three miles south-west of Liverpool. In ex- 

 amining some of the slabs of stone, extracted at the depth of above tliirty 

 feet, Mr. Cunningham observed, that their under surface was densely 

 covered w itli minute hemispherical projections, or casts in relief of circular 

 pits in tlie innnediatcly subjacent layers of clay. The origin of these 

 marks, he is of opinion, nnist be ascribed to sliower.s of rain, which fell 

 upon an argillaceous beacli exposed by Die retirmg tide, and their preserva- 

 tion to the filling up of the indentations by sand. On the same slabs are 

 impressions of feet of small reptiles, wliich appear to have passed over 

 the clay previously to the shower, since the foot-marks are also indented 

 with circular pits, but to a less degree, and the difference Mr. Cunningham 

 explains, 1)y the pressure of tlic animal havhig rendered those portions of 

 the clay less easily acted upon. That rain fell duruig remote agi's of Ihc 

 world, the author stated, no person acquainted with geology will dispute : 

 as, to the dcstructiv c and transporting agency of rain-waters many of the 

 sedimentary strata owe tlieir origin. The vast forests also, which grew at a 

 period anterior to the new red sandstone, and are now treasured up in our 

 coal fields, could not have flourished without abundant sniiplies of atmos- 

 pheric waters ; and, that the effects of drops of rain may be preserved in a 

 solid form, ho proved by reference to an account given by Mr. Scrope of a 

 shower wliicli fell upon extremely fine volcanic ashes thrown out by 



YesuYUis dvy:iBS !li« emptigu pf 1822, TJi? di'^rsi ef iniu I'vxwvtl small 



globules, which hardened into pellets, and accumulated in some places 

 at the foot of a slope, in beds a foot or more in thickness, and were 

 often so agglutinated that it reqiiired a sharp blow from a hammer to break 

 the mass. 



2. Extracts from two letters addressed to Dr. Buekland : one from Mr. 

 John Taylor, jiui., on the occurrence of a slab of sandstone containing 

 impressions of Chirotherinm Hercules at the house of Mr. Potts, of 

 Chester ; and the other by Sir Philip Egerton, on the peculiarities of the 

 impressions. When tlio slab was first laid down there was no appearance 

 of the remains which have been gradually developed by the action of the 

 weather. Sir Philip Egerton is of opinion that the weight of tlie animal 

 compressed the yielding sand near its foot, and that the print being after- 

 wards filled with the same materials, the stone became nearly homogene- 

 ous in composition. The efl'ects of tlie wcatlicr would necessarily remove 

 the softer luicompressed portions, but the denser part acted upon by the 

 animal's weight, would resist for a time the same operations, and present 

 in relief the outline of the fool. The slab contains the marks of three liind 

 and two forc-fccf, the latter bearing the same proportion in size to the for- 

 mer, as in the other species. 



?i. " On the Occurrence of Swallow-holes near Farnham, and on the 

 Drainage of the Country at the Western Extremity of the Hog's-back," by 

 George Lung, Esr/., eoniiniinicated by Mr. Lyell. — Immediately to the 

 north of Farnham, rises a chalk hill, capped by tertiary strata. No 

 perennial main-springs occur on the face of the hill, but the gulleys are, 

 for the greater part of the year, occupied by superficial land-spruigs, 

 wluch occasionally become formidable torrents. These rivulets pour down 

 the hill upon the surface of the tertiary clay, until they arrive at the chalk, 

 where they are entirely absorbed in swallow-holes, except during great 

 rains, when a portion of the water flows along channels in the chalk. 

 •Seven of these holes, between Clare Park and Farnham Park, were 

 described in detail by Mr. Long. Tlie water absorbed by two of them 

 is supposed to well out in great force at the Bourne mill-stream ; and, 

 though soft where it sinks under ground, it is hard when it re-appears. The 

 drainage, described in the second part of the paper, is eff"ected by a stream, 

 which passes throtigh a gap at Runfold, the western extremity of the 

 Ilog's-back hill, and flowing northward tluough the chalk, carries oft' the 

 surplus waters of a tract bounded on the north by the Hog's-back, and on 

 the south by a seini-cireular range of low hills, extending from Seal, on the 

 east by Crooksbury, to Moor Park, on the west. This gap in the chalk has 

 liitherto escaped the observation of geologists, but deserves to be recorded 

 among the apertures through the North Downs. 



4. "-4 Letter from Copt. Charters to Mr. Lyell, dated Cape Town, Nov. 

 12, 18.38." — During a very extensive tour through the colony. Captain 

 Charters's attention was particularly drawn to the occurrence of greenstone 

 resting upon the horizontally stratified sandstone, which constitute so largo 

 a portion of the country. The localities mentioned in the letter are in tlic 

 neighbourhood of Fort Beaufort, on the Kaftir frontier, the small toAvn of 

 Cradock on tho Great Fish Hiver, the line of route from the Tarka district 

 behind the Winterberp range to Sliiloh, and to Colesberg, near the Orange 

 River, and thence by the Sclmeeberg to Graf Reinet. In some places the 

 trap presented thick deposits, more or less traversed by irregular cracks ; 

 and, in others, heaps of weathered or spheroidal masses, resembling trans- 

 ported boulders. 



ASIATIC SOCIETY. 

 Feb. 16.— .Sir George Tuo.m.\s St.wnton, B.vrt., M.P., in the Chair. 



Mr. Wilkinson read a paper, " On the Difference between the European 

 and Indian Methods of making Steel, and on the reasons which induced him 

 to ascribe many of the properties of iron, and much of the variety in its 

 quality, to the action of electricity." After adverting to the extraordinary 

 discoveries of Professor Ehrenberg, of Berlin, who has sliovra that the bog 

 iron ore, from which the beautiful Berlin castines are made, is composed of 

 minute animals, that Tripoli powder is of a similar nature, and that the 

 ditches about Berlin aboiuid in such animals, Mr. WUkinson stated that 

 these wonderful animals had recently been found in England also, and that 

 in localities so near ,-is Hampstead and Ilighgate. Mr. Wilkinson then 

 entered into a description of the mode of manufacturing iron, and of the 

 process by Avhich it is converted into steel, both in England and India, 

 wliich differ essentially ; the English process being cliiefly exposure of the 

 iron to strong heat, in close contact with charcoal ; while the natives of 

 India put the iron into crucibles with dried branches of a certain shrub, 

 and green leaves of others. Mr. Wilkinson then adduced arguments cor- 

 roborative of the opinion, that the different properties of iron and steel 

 depend on currents of electricity, which, however, he admitted were not 

 conclusive ; and lie expressed his intention of uistituting a set of experi- 

 ments, with a view to .ascertain its truth, and its applicabihty to practical 

 purposes. He hoped shortly to obtain some specimens of Indian steel, and 

 to receive replies to several queries on the subject, sent by him to India 

 through tho medium of the Society, which would enable him to proceed 

 with more certainty. 



Jlr. Heath said, that a copy of Mr. Wilkinson's queries had been sent to 

 him by the Madras government, to whom tlie Society had transmitted them 

 in 1837 ; that his labours were at tliat time too great lo admit of his giving 

 close attention lo the .subject ; but that on his \ oyage home he had written 

 a paper, which he conceived embodied all that was required on tho subject, 

 and which he would now read. Mr. Heath's paper entered largely into tho 



nalws 9i tJis Indian pit, ami lJ;i« opci-atiyus »!' tU« natiYcs in inauulac- 



