July 25, 1901J 



NA TURE 



509 



and Mr. C. T. R. Wilson of Cambridge, had previously arrived 

 independently at the result that the air, notwithstanding the 

 exclusion of all known influences that increase its electric con- 

 ductibility, is by no means a perfect insulator, owing to the 

 existence of ions, and that the rate of dissipation increased 

 beyond its original amount in the course of a few days. A 

 possible explanation of this behaviour seemed to be that dust- 

 laden air is a worse conductor than air which is dust-free ; it 

 might be assumed that the increase of conductibility was due to 

 a gradual self-purification of the air by the deposition of the 

 dust-particles. To a certain extent this assumption is correct, 

 but as it appeared doubtful that the dissipation was due solely 

 to the air becoming dust-free, artificial means of purifying the 

 air were tried. A minute description of the apparatus employed 

 is contained in the article in question. The principal result 

 arrived at is that the gradual increase of electric conductibility 

 observed in closed air-spaces up to a certain limiting value can 

 only be very partially due to the deposition of dust, or to 

 variations of humidity. This is shown in a striking manner in 

 the abnormally high conductibility of the air in cavities, and in 

 cellars which have been closed for some time. 



Sir W. J. L. Wharton, K.C.B., the hydrographer, has 

 presented his report upon the Admiralty surveys made during 

 the year 1900, and it is published as a Blue Book. H.M. 

 surveying vessels w'ere all fully employed and good progress was 

 made in each survey ; 1 167 miles of coast line were charted, 

 and an area of 10,733 n^'l^s was sounded during the year. Dr. 

 Fowler and an assistant were taken on board the Research in 

 order to carry out, at the request of the Royal Society, zoo- 

 logical investigations in deep water about 150 miles south- 

 westward of Ushant, the object of the observations being the 

 determination of the vertical limits at which various forms of 

 marine life exist. The surveying vessel, Gladiator, was 

 taken to Larne Harbour, Ireland, with the view of ascer- 

 taining the truth of reports that the Maiden Rocks cause serious 

 local magnetic disturbances. No such effect was, however, found. 

 A chain of magnetic observations for variation was made at sea 

 by the officers of II. M.S. Kaiitbkr, on the east coast of Africa 

 off Durban, Beira, Mozambique, Zanzibar, Guardafui and the 

 Arabian coast. The observations are said io show that con- 

 siderable alteration has taken place of late years in the rate of 

 change of the magnetic declination. During a voyage from 

 Albany to Tasmania, H.M.S. Penguin obtained deep-sea 

 soundings at regular intervals 130 miles apart. The greatest 

 depth obtained was 3040 fathoms. 



The composition of alloys employed for bronze medals is 

 referred to by Sir W. C. Roberts- Austen, K.C.B., in the report 

 of the Deputy Master and Comptroller of the Royal Mint. He 

 points out that of late years a change has gradually been effected 

 in the metal used for striking medals which are known by the 

 general name of bronze. Until comparatively recently such 

 medals were invariably struck in copper, which subsequently 

 received a superficial coating mainly consisting of oxide of 

 copper, and the medal was said to be " bronzed." Such a 

 "patina" was formerly imparted to the copper medal by heat- 

 ing it in contact with oxide of iron. The Japanese have long 

 shown their remarkable skill as art-metal workers by employing 

 a wet method, by the aid of which a wide range of shades of 

 brown can be imparted to copper. The .solutions are used 

 boiling, and a variety of verdigris, known as " Rokusho," and 

 sulphate of copper are their main constituents. The Japanese, 

 moreover, are very successful in imparting a more or less trans- 

 lucent but permanent coating to the copper, which in fine 

 examples of their art reveals the crystalline structure of the 

 metal beneath the "patina." Sir William Roberts- Austen states 

 that in the years 1S97-98 more than 28,500 medals, in com- 

 memoration of the Jubilee of Her Majesty the late Queen, were 

 NO. 1656, VOL. 64] 



so treated, and the specimens which have oeen preserved in the 

 Mint show no diminution in the brilliancy of the tints which 

 were originally imparted to them. Many European mints are 

 following the Paris Mint in efforts to replace pure copper by 

 copper alloyed with other metals. Analyses of coins of the 

 reign of Hadrian and Trajan show that the alloys contained 

 about 87 or 88 per cent, of copper and 7 to 1 1 per cent, of 

 zinc, the remainder being made up of tin, lead, iron and silver, 

 w'ith traces of arsenic and antimony. Sir William Roberts- 

 Austen remarks that modern medallists are working with alloys 

 which resemble those from which the coins mentioned were 

 struck, so that the medallist of to-day is returning to the ideas 

 developed in ancient Rome. 



A NEW rangefinder, invented by Prof. G. Forbes, F. R.S., was 

 I on view at the Bisley rifle meeting. The want of a rangefinder 

 j that is portable and workable, that has not more than two per 

 I cent, inaccuracy at 3000 yards, and that does not require a 

 I telescope so large as to require a stand, is much felt for infantry 

 j work, especially with maxims. All these conditions, says the 

 Times correspondent at the meeting, are met by the one in 

 question. It consists of a folding aluminium base, six feet in 

 length, which can be folded in the middle and strapped across 

 the back, and a field-glass carried in the usual fashion. The base 

 is a square tube, hinged at the middle. Each half has at each 

 end a doubly reflecting glass prism. The rays of light from a 

 distant object strike the outer pair of these four prisms, are 

 reflected at right angles along each tube, and are then reflected 

 at the two middle prisms into the two telescopes of the binocular, 

 which can be easily fixed to the centre of the base when in use 

 in directions parallel to the original rays intercepted by the outer 

 prisms. By the measurement of the angle between these rays 

 the distance of the object looked at is determined. This angle 

 is measured by two vertical wires, one in each telescope, seen by 

 the two ej'es. One of these wires is fixed, the other moved by a 

 micrometer screw until the two wires appear as one at the same 

 time that the object is seen distinctly. The instrument gives the 

 distance, in the hands of an ordinary observer, at 3000 yards 

 to within 60 yards, at 1500 yards to 15 yards. The 6 ft. base 

 folds to 3 ft. 3 in. and weighs under 3 lb. 



In the Revue gent'rale des Sciences, Dr. Guillaume, of the 

 Bureau des poids et mesures, discusses the laws of radiation in 

 reference to their application to incandescent mantles. Dr. 

 Guillaume considers that the high intensity of the Auer light is 

 due partly to the fact that the coefficient of radiation of the 

 mantle is exceptionally high towards the blue end of the flame, 

 partly to the temperature of the flame itself being, as the author 

 shows, higher than has been commonly supposed, and partly to 

 the density of the radiating substance being largely in excess of 

 that of the citbon in an ordinary combustion flame. The 

 high temperature of the mantle is probably attributable to the fact 

 that its coefficient of radiation decreases rapidly tow'ards the red 

 end and infra-red of the spectrum, so that the total radiation is 

 relatively small in comparison with the radiation of rays of short 

 wave-length. Dr. Guillaume quotes the work of Messrs. 

 Le Chatelier and Boudouard, and suggests that the coeflicient 

 of radiation of the mantles for infra-red rays presents an 

 interesting field of study. It seems probable that as the wave- 

 length increases, the coefficient may decrease to a minimum and 

 may increase again in a region considerably distant from the 

 visible spectrum. The substances used by von Welsbach thus 

 exhibit gaps in an easily explored region of their emission- 

 spectrum, and we may expect to obtain, with little difficulty, 

 results difl'ering considerably from those furnished by the study 

 of substances whose radiation is more nearly uniform. 



The skin of the okapi, the new mammal discovered by Sir 

 Harry Johnston in the Semliki Forest betw'een Lakes .-Albert 



