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The manufacture of optical glass
Oct., 192I.] NOTES FROM NELA RESEARCH LABORATORY.
537
has been encountered in obtaining a satisfactory white paint which was tenacious and permanent in color. An investigation carried out by the author at the Bureau of Standards several years ago resulted in a very satisfactory paint. The formula for the paint, together with full details as to preparation and use, will soon be published in the Transactions of the Illuminating Engineer-
ing Society. CLEVELAND,OHIO, August 16, 1921.
Stereoscopic Portraits.--Das Atelier des Photographen has an article on this subject, referring to an invention nlade in 1853 , by a Philadelphian, J. F. Mascher, who took out a patent in that y e a r for an " Improvement in Daguerreotype Cases." The main feature of his invention was the provision of a small convex lens attached in a movable flap to the case containing the picture so that it could be viewed somewhat magnified, but the special feature was the making of two portraits by stereoscopic methods and providing a pair of lenses for securing the effect. The German writer figures the apparatus, and states that the pictures show an exaggerated solidity, and were probably made by a collodion film on glass, being, therefore, of the nature of the ambrotype, which was much in vogue prior to the introduction of the paper positive. A picture of the apparatus is given. It is interesting to note that one of the stereoscopic portraits is in the possession of The Franklin Institute. It was evidently made by a stereoscopic camera, for the two pictures have no~:iceable, though slight, differences and when viewed with the lenses show a strong, indeed excessive, solidity. The claim in the patent does not specifically refer to the application of stereoscopy, and the inventor put on the market many cases with single pictures. The attention given to the matter indicates that the Germans, like the French, are taking nmch interest in the revival of stereoscopic work, a special field which has been the subject of a good deal of discussion lately in the projection on the screen of the effect of solidity. H.L. The Manufacture of Optical Glass.mThis problem has received a great deal of attention of recent years. The dependence of the world at large upon Germany for glass suitable for the construction of many optical instruments for warfare and research w.as brought to notice when the war broke out, and it became necessary for the Other belligerent nations to establish industries for the purpose. The subject is revived by the publication of a pamphlet by the Goerz Company, being a reprint of an article by Dr. F. Weidert (of the
538
CURRENT T o r s o s .
[J. F. I.
Goerz Company) originally appearing in a Berlin engineering j our -~ hal. The article is illustrated with eight full-page plates, giving views of certain parts of the factory of that firm. The title is " Herstellung und E igenschaften des Optischen Glasses." One point of interest is the statement that just before the breaking out of the war, only three establishments capable of producing optical glass existed. These were: Chance Brothers in England, Parra-Mantois in France and Schott and Company in Jena. The product of the English firm was principally for mirrors, of which it was the larges.t European manufacturer, but its true optical glass was in small amount. The Paris firm produced a high-class material but not in large amount. The Jena firm was not deemed sufficient for the needs of Germany, and shortly before the war another German establishment was founded. The pamphlet gives an account of the principal features of the establishment of the German glass industry, in which the familiar names of Steinheil and Fraunhofer appear. H.L. N e w D e t e r m i n a t i o n s of the D e n s i t y of the Air at Geneva. A. TRE~TI~ARDT. On the Density of the Air at Madrid and its Slight Variations. MOLES, BATUCCAS AND PAYA. (Co*nptes Rendus, June 2o, I 9 2 I . ) - - C o n t r a r y to the general belief the density of the air under standard conditions is not strictly constant. At the same place it appears to be less by some tenths of a milligram per liter during periods of high barometric pressure. This was shown to true for the air of Geneva by Guye and his collaborators in I9IO, and was confirmed two years later for the same place and six years later for Cleveland, Ohio. Near a pressure of 760 mm. flasks were filled with air at zero from which water vapor and carbon dioxide had been removed. The previous results were confirmed by the Swiss as well as by the Spanish observers. The latter plotted both the changes in barometric height and in density for considerable part of a year. It is noteworthy that when one of these changes increases the other decreases almost unfailingly. At one period of apparent exception to this statement the weather was clear and the sunshine strong. This led to the suspicion that ozone might be the cause of the divergence. When the air was treated in such manner as to free it from ozone its density was found to cease to be exceptional. The average of the determinations in Geneva was 1.29269per liter and in Madrid 1.293o 3. In view of the outcome of the experiments it is suggested that air should not be used as a standard for getting the densities of other gases. The quantities concerned are, to be sure, small, but let it be remembered that other minimal differences of density led to the discovery of argon. G. F. S.
537
has been encountered in obtaining a satisfactory white paint which was tenacious and permanent in color. An investigation carried out by the author at the Bureau of Standards several years ago resulted in a very satisfactory paint. The formula for the paint, together with full details as to preparation and use, will soon be published in the Transactions of the Illuminating Engineer-
ing Society. CLEVELAND,OHIO, August 16, 1921.
Stereoscopic Portraits.--Das Atelier des Photographen has an article on this subject, referring to an invention nlade in 1853 , by a Philadelphian, J. F. Mascher, who took out a patent in that y e a r for an " Improvement in Daguerreotype Cases." The main feature of his invention was the provision of a small convex lens attached in a movable flap to the case containing the picture so that it could be viewed somewhat magnified, but the special feature was the making of two portraits by stereoscopic methods and providing a pair of lenses for securing the effect. The German writer figures the apparatus, and states that the pictures show an exaggerated solidity, and were probably made by a collodion film on glass, being, therefore, of the nature of the ambrotype, which was much in vogue prior to the introduction of the paper positive. A picture of the apparatus is given. It is interesting to note that one of the stereoscopic portraits is in the possession of The Franklin Institute. It was evidently made by a stereoscopic camera, for the two pictures have no~:iceable, though slight, differences and when viewed with the lenses show a strong, indeed excessive, solidity. The claim in the patent does not specifically refer to the application of stereoscopy, and the inventor put on the market many cases with single pictures. The attention given to the matter indicates that the Germans, like the French, are taking nmch interest in the revival of stereoscopic work, a special field which has been the subject of a good deal of discussion lately in the projection on the screen of the effect of solidity. H.L. The Manufacture of Optical Glass.mThis problem has received a great deal of attention of recent years. The dependence of the world at large upon Germany for glass suitable for the construction of many optical instruments for warfare and research w.as brought to notice when the war broke out, and it became necessary for the Other belligerent nations to establish industries for the purpose. The subject is revived by the publication of a pamphlet by the Goerz Company, being a reprint of an article by Dr. F. Weidert (of the
538
CURRENT T o r s o s .
[J. F. I.
Goerz Company) originally appearing in a Berlin engineering j our -~ hal. The article is illustrated with eight full-page plates, giving views of certain parts of the factory of that firm. The title is " Herstellung und E igenschaften des Optischen Glasses." One point of interest is the statement that just before the breaking out of the war, only three establishments capable of producing optical glass existed. These were: Chance Brothers in England, Parra-Mantois in France and Schott and Company in Jena. The product of the English firm was principally for mirrors, of which it was the larges.t European manufacturer, but its true optical glass was in small amount. The Paris firm produced a high-class material but not in large amount. The Jena firm was not deemed sufficient for the needs of Germany, and shortly before the war another German establishment was founded. The pamphlet gives an account of the principal features of the establishment of the German glass industry, in which the familiar names of Steinheil and Fraunhofer appear. H.L. N e w D e t e r m i n a t i o n s of the D e n s i t y of the Air at Geneva. A. TRE~TI~ARDT. On the Density of the Air at Madrid and its Slight Variations. MOLES, BATUCCAS AND PAYA. (Co*nptes Rendus, June 2o, I 9 2 I . ) - - C o n t r a r y to the general belief the density of the air under standard conditions is not strictly constant. At the same place it appears to be less by some tenths of a milligram per liter during periods of high barometric pressure. This was shown to true for the air of Geneva by Guye and his collaborators in I9IO, and was confirmed two years later for the same place and six years later for Cleveland, Ohio. Near a pressure of 760 mm. flasks were filled with air at zero from which water vapor and carbon dioxide had been removed. The previous results were confirmed by the Swiss as well as by the Spanish observers. The latter plotted both the changes in barometric height and in density for considerable part of a year. It is noteworthy that when one of these changes increases the other decreases almost unfailingly. At one period of apparent exception to this statement the weather was clear and the sunshine strong. This led to the suspicion that ozone might be the cause of the divergence. When the air was treated in such manner as to free it from ozone its density was found to cease to be exceptional. The average of the determinations in Geneva was 1.29269per liter and in Madrid 1.293o 3. In view of the outcome of the experiments it is suggested that air should not be used as a standard for getting the densities of other gases. The quantities concerned are, to be sure, small, but let it be remembered that other minimal differences of density led to the discovery of argon. G. F. S.