July 19, 1900] 



NATURE 



273 



fully equipped, but in 1887 additional lecturers were appointed, 

 and as the advantages of the course came to be appreciated, the 

 number of students increased rapidly, and the attendance is now 

 very large. Through the energy of Prof. Ulrich the models and 

 appliances which had been procured from time to time became a 

 valuable collection, especially in the mineral department, to 

 which he was constantly adding from his own private collections 

 of minerals and stones. 



The Committee on Indexing Chemical Literature presented 

 their report of progress at the recent meeting of the American 

 Association. From it we learn that Dr. Alfred Tuckerman has 

 completed and sent to the Smithsonian Institution a supplement 

 to his index to the literature of the spectroscope, which covers 

 the period from 1887 to 1899. Dr. H. Carrington Bolton's 

 second supplement to his select bibliography of chemistry, 

 containing a list of 7500 chemical dissertations, is passing through 

 the press ; it will form a volume of the Smithsonian Mis- 

 cellaneous Collections. Mr. A. G. Smith, of Cornell Univer- 

 sity, is engaged on an index to the literature of selenium and 

 tellurium, which, it is expected, will be completed this summer. 

 Dr. Frank I. Shepherd proposes to make a bibliography of the 

 alkaloids. Mr. Frank R. Fraprie contemplates preparing an 

 index to the literature of lithium. 



In the Revue GenJrale des Sciences, M. Louis Olivier gives 

 some further particulars of Poulsen's " telegraphone," which is 

 attracting attention at the Paris Exhibition. He describes 

 several devices for increasing the volume of sound, or " intensi- 

 fying " the record, to use the language of the photographer. 

 The steel band with the consequent poles, which forms the 

 original record, is made to pass between the poles of an electro- 

 magnet, which transfers the record to another band. This may 

 be done several times over, and the record taken simultaneously 

 from all the bands. In another arrangement the record is 

 intensified by passing it very rapidly through the second magnetic 

 field, which, as we know, has the effect of increasing the induced 

 currents, and therefore also the intensity of the secondary 

 record. 



A NO\'EL type of Newton's rings is described by Mr. A. C. 

 Longden in the current number of the American Journal of 

 Science. They are prepared by exposing a glass plate to the 

 kathode rays emitted from a small globule of selenium. The 

 film thus deposited is thickest at the point exactly opposite the 

 globule, and tapers off towards the sides. The result is a film 

 in the shape of a very flat lens, the upper and lower surfaces of 

 which reflect light somewhat in the same manner as the upper 

 and lower surfaces of the air film in Newton's device, with the 

 difference, however, that in Mr. Longden's arrangement the film 

 tapers outward instead of inward. Hence the rings increase in 

 breadth and brilliancy away from the centre, and the order of 

 the colours is reversed. The effect is described as very pretty. 



The annual list of the staffs 01 the Royal Gardens, Kew, and 

 of botanical departments and establishments at home, and in 

 India and the Colonies, in correspondence with Kew, has just 

 been issued as an appendix to the Bulletin of Miscellaneous 

 Information. We notice that sixty-six of the officers of the 

 various botanic gardens have been trained at Kew, and seven- 

 teen others were appointed on the recommendation of the director 

 of the Royal Gardens. With so many efficient observers distri- 

 buted over our possessions it is not surprising that Kew is able 

 to be of great service to the Elmpire as well as to science. 



Plague has now been established in Sydney for several 

 months, and in an address delivered before the New South Wales 

 Branch of the British Medical Association, Dr. Frank Tidswell 

 of Sydney recently discussed a variety of interesting questions 

 relating to the disease. Referring to his remarks on rats, the 

 NO 1603. VOL. 62 1 



Lancet points out that there are instances which show that the 

 presence of a plague-rat is often responsible for the illness in 

 man. For example, a number of dead rats found one morning 

 in a cotton factory at Bombay were removed by twenty coolies. 

 Within the three following days about half of them fell sick with 

 plague, whilst those in the store who had not touched the rats- 

 were not affected. Again, the coachman of an English family 

 in Bombay found a dead rat in a stable and removed it. Three 

 days later he fell sick with plague and died in a few hours, no 

 other person in the same house being affected. Many persons^ 

 however, have caught plague without handling plague rats, and 

 many persons have handled plague rats without catching plague. 

 To explain this difficulty Simond has suggested that the infection 

 is carried by the fleas natural to the rats. Perfectly healthy rats, 

 harbour very few fleas, and are very expert in removing them, 

 but fleas are abundant on sick rats. After death, as the body 

 becomes cold, the fleas leave it. In this way Simond accounted 

 for the fact that a plague rat may be handled with impunity some 

 hours after death. If the fleas from the dead rat reach another 

 rat or a human being, they may inoculate the bacilli they acquired 

 by ingesting the blood of their former host. In some of Simond's 

 experiments sick and healthy rats in separate cages were enclosed 

 in a glass jar, and it was found that when no fleas were present 

 the healthy animals did not become infected. 



Colour photometry is a subject that Sir William Abney has 

 made his own, and in his last communication to the Royal 

 Society he describes a method of estimating the luminosity of 

 coloured surfaces that is especially applicable when the source 

 of light is a large surface, such as the sky. la " Colour Photo- 

 metry, Part iii."it was shown that only one ray of the spectrum, 

 a greenish-yellow, progressed in luminosity at the same rate as^ 

 white light. If, for example, red, greenish-yellow, blue and 

 white lights are made of equal luminosity, and the illuminating 

 beams are simultaneously and equally reduced in intensity, the 

 luminosity of the red will diminish the mast rapidly, that of the 

 blue the least rapidly, the other two remaininj; equal. More- 

 over, the colour disappears more quickly than the luminosity 

 (except in the case of pure red), tending towards greyness, so- 

 that colours of feeble luminosity are more easy to match thia 

 bright colours. The new method of colour photometry is based 

 upon these facts. By means of concentric rotating discs, which 

 are, when necessary, slit radially and interlaced, the proportion 

 of black and white that matches first a green and then a yellow- 

 disc is determined. The comparisons are facilitated by observinjf 

 the rotating discs through a "black transparent medium," such 

 as an unstained developed photographic film, which may be so 

 dense that the colour practically disippears, giving place to a 

 dull grey. The value of a red disc is ascertained by interlacing 

 it with the green and blue discs to produce a grey, which is ther> 

 matched with the black and white. Thus, having three standard 

 colours of known values, the luminosity of any other colour can 

 be ascertained by substituting a disc of it for one of the standard 

 colours to produce a grey, and matching the grey as before. 

 The results given by this method agree closely with those 

 obtained by the method previously described by the author. 

 Sir William Abney has in this way determined the luminosities 

 of various coloured surfaces and calculated the amount of 

 black necessary for each, so that they shall be reduced to equil 

 luminosity. He has then prepared a disc divided into several 

 annuluses, each partly coloured and partly black, so that when, 

 rotated the whole appears of equal luminasity when illuminated 

 by the light for which it is calculated. By the selection of 

 suitable colours such a disc is a very convenient and effective 

 test for any defect in either the cjlour sensitiveness of a photo- 

 graphic plate, or in the coloured screen used to compensate its- 

 inherent deficiencies in this mitter. For the rotating disc, 

 which is equally luminous throughout, will give, when the 



