June iS, 1891J 



NATURE 



155 



meteorological measurements ; Dr. K. Feussner and Dr. 

 St. Lindeck, on electrical measurements ; Dr. O. Lummer 

 and Ur. E. Brodhun, on optical measurements, including 

 photometry ; Dr. F. Foerster and Dr. F. Milius, on 

 chemical analysis of glass. 



We gather from the Director's Report above referred 

 to, that the Institution has provided itself with funda- 

 mental standards of length and mass ; with primary 

 thermometers and barometers ; with electrical standards 

 of resistance, current, and pressure ; and with apparatus 

 for testing the flashing point of petroleum and inflammable 

 Hquids. Its metrological work for the public has in- 

 cluded the proving of clinical thermometers, pyrometers, 

 aneroid barometers, manometers, alcohol thermometers 

 for low temperature, and thermometers for chemical 

 research. 



In October 1888, the official testing of thermometers 

 was transferred from the Normal Aichungs Commission at 

 Berlin to the Imperial Institution, and all thermometers 

 are still tested on the basis of the regulations laid down 

 by the Commission on November 10, 1885 5 excepting 

 that, in place of basing the errors of scientific thermo- 

 meters on a mercurial thermometer, thermometer readings 

 are now reduced to the more accurate scale of the air- 

 thermometer or hydrogen-thermometer. 



The use of thermometers for determining pressures, or 

 altitudes, &c., on the occasion of journeys of exploration, 

 &c., seems of late to have increased, for many such have 

 been already presented for examination at the Institu- 

 tion. If the thermometers are made of Jena glass (or 

 of other hard thermometer glass), it would appear to be 

 possible to ascertain pressures with but little trouble to 

 ± 0-25 millimetre. The necessity for using proper 

 glass is shown in an experiment carried out at the In- 

 stitution with two thermometers, Nos. 42 and 43, made of 

 ordinary Thuringian and crystal glass. On September 7, 

 1888, the corrections of these thermometers at 87° C. 

 were found to be — 



No. 42, - o°-o5 ; No. 43, - o''-24 C. 



The thermometers were then heated for 15 minutes to a 

 temperature of 100'' C. ; they were then allowed to cool, 

 and subsequently retested on September 10, when their 

 errors were found to be — 



No. 42, + o^-o8 ; No. 43, - o^'og C. 



Such variation in the reading of a thermometer after 

 its exposure to a high temperature would unfit it for use 

 in the exact determination of pressures or altitudes. 



With reference to the testing of various sorts of glass Dr. 

 F. Milius points out that Weber's process, generally made 

 use of, and which consists in exposing the body to be exa- 

 mined to an atmosphere of muriatic acid vapour for a space 

 of twenty-four hours, is not always trustworthy. Thus, ac- 

 cording to the quality of the glass, it appears to be 

 covered more or less, after exposure to the acid vapour, by 

 a thick rime (or hoarfrost) ; and that although the ex- 

 perienced observer finds Weber's method tolerably certain, 

 yet the less experienced observer may sometimes be left 

 in doubt, particularly where rough surfaces are treated, 

 as to whether the rime exists or not ; Dr. Milius therefore 

 proposes an optical form of test other than that of the 

 muriatic acid test, as is explained at length in his paper. 



Dr. Milius, in conjunction with Dr. F. Foerster, has also 

 investigated the solubility, in water, of potash and soda 

 glass, particularly with reference to Schott's experiments 

 as to the capacity of potash water-glass for absorbing 

 water without losing its vitreous quality. This latter fact 

 can be ascertained by keeping pulverized water-glass 

 under water, when, as in the case of hydraulic cement, a 

 hardening of the paste begins to take place. This pro- 

 cess is connected with a development of heat ; in the 

 case of water-glass in which there was one atom of po'.ash 

 to three of silicic acid it was observed at the Institution 



NO. I I 29, VOL. 44] 



that within a quarter of an hour the moistened matter had 

 been heated 10° Centigrade, and it became hard in one 

 day ; if the proportion of silicic acid is larger, the glass 

 requires from two to three days for solidification. Their 

 researches appear to show that for purposes con- 

 nected with mercurial electrical standards, the glass used 

 should be very little soluble in water and acids ; hard 

 glass, for instance, which had a base of soda, and not 

 potash, being little hygrometric. 



In the important field of electrical measurements, the 

 Institution appears also to be doing good work. It is 

 preparing to undertake the verification of all kinds of 

 apparatus ; including voltmeters, ammeters, meters for 

 the measurement of power and efficiency, galvanometers, 

 and resistance coils. 



In the field of practical photometry we have to com- 

 pare the intensities of different sources of light as ex- 

 perienced by the eye ; but unfortunately we have not, 

 even for commercial purposes, any satisfactory method 

 by which intercomparisons may be made between the 

 relative intensities of coal-gas, electric and oil lights re- 

 spectively. In practical photometry much is being done 

 in this country by Abney, Vernon-Harcourt, Chaney, and 

 others, as well as by Lummer, Brodhun, and others in 

 Germany, but as yet no standard photometer has been 

 produced. The standard light is still also the ancient 

 " sperm-candle," and the method of comparison is still 

 the old-fashioned " grease-spot " Bunsen photometer 

 more or less modified. The German authorities appear 

 to be fully alive to the necessity of improvement in this 

 field of technical research ; and have investigated M.Violle's 

 incandescent platinum-standard of light, and also the 

 Hefner lamp and Aubert's apparatus ; and for electrical 

 light purposes they have followed a form of standard 

 glow lamp. 



Among the papers above referred to, we notice also one 

 by Dr. Loewenherz, on the testing of tuning-forks. The In- 

 stitution undertakes the testing of tuning-forks, on payment 

 of a small fee, the object of the examination being to 

 ascertain the correctness of the height of the tone of 

 the fork in terms of an international diapason ; or the 

 number of the vibrations of the fork per second, at the 

 temperature of 1 5° Centigrade, the pitch of the note A 

 being fixed at 435 entire vibrations per second, or 870 

 half or single vibrations according to the French method 

 of counting. Tuning-forks sent to the Institution for 

 examination are required to be constructed in accordance 

 with conditions laid down by the Institution. Unity of 

 pitch is of fundamental importance in music and in the 

 construction of musical instruments, and it is to be 

 desired that some authoritative testing of tuning-forks 

 might be similarly undertaken in this country. 



In metallurgy the work of the chemical laboratories of 

 the Institution does not appear to be extensive ; it has 

 included more particularly analyses of the metals pla- 

 tinum, cadmium, and rhodium. In the Physical Labora- 

 tory, measuring instruments of precision for workshop 

 use, such as speed and power indicators, screw-thread 

 gauges, have also been examined by the Institution ; and 

 its geodetical work has included the verification of instru- 

 ments of precision for General Schreiber, of the Imperial 

 Prussian Land Survey. The department has undertaken 

 also the verification of polariscopes, lenses, prisms, and 

 other optical instruments, to a limited extent. 



The above observations may serve to show that the 

 Institution is alike prepared to verify a standard — as a 

 measurer of electrical resistance— with the utmost accu- 

 racy, or to test an instrument for common purposes — as a 

 gas meter. How far the Institution maybe self-supporting 

 is not stated in the Director's Report ; but as the demands 

 for verification work of this kind are largely voluntary, it 

 would appear to be evident that the excellent staff of the 

 Institution could not be maintained unless it received 

 valuable support from the State. 



