The photographic news

• Bandzählung: 6.1862
• Erscheinungsdatum: 1862
• Sprache: Englisch
• Signatur: F 135
• Vorlage: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: SLUB Dresden
• Rechtehinweis: Public Domain Mark 1.0
• URN: urn:nbn:de:bsz:14-db-id1780948042-186200003
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• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
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• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

March 14, 1862.] THE PHOTOGRAPHIC NEWS. 123 18G2. 3. of inch an 51-23 vent tb icnts o9 recen edwi * American Journal of Science (2), iv. 388 and v. 1. y the T ion of s reat in mouut it to K satisfat Id 1’3 1 1 62-34 62'74 65-75 81-97 85-11 89-62 97-68 “Single German” window glass Thick English plate Crystal plate “Double English” window glass “Double German” ditto English crown Are "J is eq" t frow' re then ne add ve mo 1 size 0 he pre who y simp r-plat h a ft lly so’ b show then V t whid J i I IB ? GLASS OPERATING ROOMS. BY M. VOYTOT. HIMERrO, when a photographer has wished to construct an operating room, his first care has been to obtain a northern aspect entirely sheltered from the sun’s rays; experience had proved that these rays caused much inconvenience, therefore, it was concluded, they must be entirely avoided. But of late years photography has taken such an exten sion, that most available northern aspects have become occu pied, and the photographer is now content to acquire any position, no matter what the aspect may be, if otherwise suitable. Fully satisfied that the progress of photography will not be checked by a cause which appears to me quite accidental, I have not hesitated to instal myself in a locality, under conditions which most photographers would have considered impossible. I have constructed, in a full south ern aspect, on the sixth storey, an operating room, 30 feet long by 10 feet wide, and 12 feet high. As may be sup posed, the light is very strong, and sometimes even unsup portable. • racy. We may also mention that none of the measurements (of the distance of the photometer from the standard candle) obtained by actual experiment were calculated—i. e., reduced to their equivalent in candles—until the whole series of IXDS ’ D Gu 4-27 per cent. 6-15 8’61 „ 9-39 13-00 „ 1308 34-48 metric method, essentially like Rumford’s, Bouguer mea sured the loss of light in the beam of a candle compared with a flambeau and also with the light of the full moon in passing through 16 thicknesses of common window glass having an united thickness of 0'85 inch. The mean loss of light shown by these trials was as 247 : 1 or over 99 per cent, of the whole quantity. Six plates of the purest mirror plate glass, having an united thickness of 15'128 millimetres diminished the light in the ratio of 10 : 3 occasion ing a loss of about 70 per cent, of diffused daylight. A mass of very pure glass about three inches thick diminished the light only about half the latter amount owing to its being in a single mass, and not cut up into many planes. He also measured the absorbing power of sea water for light, and found as the results of experiments made in France, and of observations also in the torrid zone, that at the depth of 311 French feet the light of the sun would be equal only to that of the full moon, and at the depth of 679 feet would wholly disappear. He estimated the transparency of air as 4 575 times greater than that of seawater, and from the properties of a logarithmic curve, whose functions he had determined experimentally, he sought to fix the outer limits of the at mosphere. Bouguer was an expert geometer, and sustains all his conclusions by mathematical demonstrations. His results seem to have received less attention than they merit, the only reference to his researches we have seen being by Daguin, in his excellent “ Trait de Physique,” vol. iii. p. 300. We should not omit, in connection with this, to refer to the very interesting observations of Draper* on the spec trum, formed by means of a platinum wire heated gradually from dull redness to perfect whiteness by a voltaic current. He observed the red part of the spectrum to appear first, and as the heat and brilliancy of the wire increased the other colours of the spectrum appeared after the violet. This re sult perfectly harmonises with the views above expressed. C. W.—A specimen of glass has been forwarded to us for examination in the spectroscope. It is a silver-coloured flashed glass, of the peculiar deep orange colour which expe rience has shown to be so adiactinic. Examined in the in- strument it is seen to cut off all the higher actinic rays in a most perfect manner, but upon attentive scrutiny in a bright light we can detect traces of the higher green rays struggling through. As these are actine on bromide of silver it might theoretically be injudicious to make use of this glass, but the proportion of active rays transmitted is so small, that if the window be not exposed to very bright incident light it might be used with safety. At the same time it should be remembered that any future increase in the sensitiveness of the photographic media would increase the possibility of in jury from the use of such a glass. experiments was completed, and that no comparison of the results among themselves or with those of Mr. King was made until each result was calculated as given below. Whatever the experiments may be worth, therefore, they have at least the merit of being entirely independent and he pritl vith tb‘ 1 it, a* probabl ‘ o J r nis plat wholly unbiassed. lor convenience of reference, we will ti v sug arrange the results in a tabular form. The first column copper gives the description of glass employed, the second column is marb the thickness of the sheet, and the the third column the loss of light in per centages, taking the whole amount of inci dent rays at 100. aA 19 01 -l ro-uuU nt wniun •nE lump is of A burning, and thus aid in the general illumination of the E Ixo” - ■ ■ ■ ’ ■ ■ ILAsS • vas co" I power 0 - " room. The meaning here attached to the term is, however, perfectly evident, and there can be no doubt that the numbers given above express, as accurately as the circum- stances of the case will admit, the actual diminution of the ib amount of light falling, for example, upon the pages of a book held near to its source, which would be occasioned by the interposition of the shade enumerated in the table. Referring to these experiments, Mr. B. Silliman, jun., 8uggests that the great loss of light proved by these experi alist " inents may be in part, at least, accounted for by the con- - Version of a portion of the light into heat, an effect per- 3d fro. hotly in harmony with the theory of transverse vibrations " applied to explain the phenomena of the polarization of “sat. On this theory heat and light are different effects Produced by one ami the same cause, and they differ physi- . Sally only in the rapidity and amplitude of their vibrations, er ho 1 .’“be screen through which the vibrations of light are pro- KipG.Pagated serves to diminish, first the rapidity of the vibra- y eigOBons requisite to produce the most refrangible rays, and in :, whi°Proportion as the transparency of the screen is diminished ng) a."! any cause, inherent or superficial, this arrest becomes t appezClore and more complete. Hence, the loss of light from he glgPolished screens is small compared with that observed in ipon tIsteens of opaline or roughened glass. It would be instruc- no sShye to examine the spectrum obtained from a pencil of rays ts motnder each of the cases given by meansofa complete quartz re m°"ain of prisms and lenses. 3unse" L The subject of airsorption of light by screens hag long re ac®" "ce been carefully examined by Bouguer. By a photo- 1Strov? On looking over the above results the reader cannot fail satisfoe 1 notice the enormous resistance to the passage of light which is offered by ground-glass. This is certainly worth | the attention of photographers and others who are accustomed I to employ this medium for glazing their operating-rooms, j or, indeed, f or a ny purpose where plenty of light is desirable. The term “ loss of light ” may be objected to as being Scarcely appropriate, for a very considerable portion of the ight not transmitted by a glass shade might be reflected Against the walls of the apartment in which the lamp is Orange coloured window glass “ Berkshire” enamelled, i.e., ) ground only upon portions 1 of its surface, small figure ) .. - “Double German.” ground... he pW 1 “ Berkshire," ground a tint % "Single German,” ground ... stead d Green coloured window glass hl Purple coloured ditto Rubycoloured ditto i , si Porcelain transparency 1 l.alwat (Tyrolese Hunter) J Ris’] 0.1.