558 



NATURE 



{Oct. 25, 1877 



yet a weighing by the long-arm balance occupies twice as much 

 time as one made witli the short-arm balance. Consequently 

 great economy of time is obtained by the use of a short- 

 arm balance. Prof. BarlT's process for preventing the corro- 

 sion of iron appeared to the department to be likely to 

 prevent the oxidation of Standard weights made of iron. Prof. 

 Baiff has undertaken to submit some specimens of iron weights 

 to this proces.";, and it is intended to place these weights in the 

 hands of some local inspector of weights and measures so that it 

 may be ascertained whether iron Standard weights thus protected 

 could safely be used in place cf the expensive bronze or brass 

 Standard weiglits at present used. The Report refers to several 

 other points connected with the working of the department, one 

 of importance to the general public being its operations in con- 

 nection with the testing of gas meters. 



Mr. a. Ri.ngwood, of Adelaide, South Australia, publishes 

 a plan by which one observer may measure the height of llie 

 clouds. The observer is to note the altitude and azimuth of the 

 cloud, the azimuth of the cloud's shadow, and the spot in the 

 surrounding country wliere tlie shadow falls ; from this la^t 

 observation by means of a map he can find the distance of the 

 sh,idow from him. From these elements, together with the 

 altitude and azimuth of the sun, a variety of expressions for the 

 hc'ght of the cloud can be deduced. The method is equivalent 

 to taking observations at each end of a base whose length is the 

 c'iJance of the shadow from the observer, the observer at 

 the shadow end of the base being the sun. The difftculty of 

 recognising the shadows of individual clouds and the compara- 

 tively short time in each day during which it would be possible 

 to do so, joined with the fact that the higher clouds, such as 

 c'rrus and cirrocumulus, hardly ever cast defined shadows, must 

 prevent the method from becoming generally useful ; but still 

 tliere is this to be said for it, that if in an observation the base, 

 i.e., the distance of the cloud's shadow from the observer, is 

 It ng, a good measure of the height of the cloud may be got with 

 comparatively rougli observations of the other elements. 



The singing of mice is a phenomenon which was recently 

 affirmed by Dr. Berdier in a letter to La Nature. A distinguished 

 lierpetologist, M. Lataste, suggested that he may have made con- 

 fusion with the singing of a raniform batrachian, the Bomlunator 

 i^ncus, but Dr. Berdier said there was no marshy ground near the 

 room in which he had heard it, and he stuck to his assertion. His 

 observation has been confirmed |at a recent meeting of the French 

 Societe d'AccIimatation, by M. Brierre, who stated that he, with 

 several others, had heard mice sing at Saint-Michel-sur-l'Heron 

 (in Vendee), in £851-1853. The singing (which was .it first 

 attributed to reptiles) came from an old cupboard bought in a 

 market-place, and concealing mice. It was about sunset that the 

 sounds generally commenced. M. Brierre soaped the joints and 

 the wood so that he might open the cupboard suddenly without 

 noise. He did the latter one evening soon after the sounds had 

 commenced, and succeeded in observing, for about a minute, the 

 movements of the throat of a mouse, which emitted a song like 

 that of a wren, the snout being elongated and held up in the air, 

 as a dog does when he howls. He seized the animal with his 

 hand and called others to see it, but it got off. The singing was 

 resumed the same night and those following. M. Brierre is unable 

 to attribute the singing of the mice (as Dr. Berdier does) to imita- 

 tion of that of canaries, for he had no birds in the house, nor had 

 the previous proprietor of the cupboard any. 



In describing some recent falls of meteoric stones in America, 

 Mr. Lawrence Smith has pointed out {Comptes Rcndus) that in the 

 last eighteen years there have been, in the United States, twelve 

 falls of meteorites which have been collected ; and he notes the 

 remarkable fact that eiglit of the meteorites, representing more 

 than 1,000 kilogrammes of matter, have fallen in the region of 

 the Western Prairies, and on a surface which does not exceed one- 



eighth of the extent of the United States. This cannot evidently 

 be attributed to there being a dense population and numerous 

 observers (a consideration sometimes urged). Still more striking 

 is the circumstance that in the last sixty years there have been 

 twenty falls of meteorites observed in the United States, of 

 which ten, or the half, have fallen in this same region ; and, 

 moreover, these falls have brought about 1,200 kilogrammes of 

 mineral substance, a quantity twenty times greater than that of 

 the ten other falls recorded as having occurred outside of this 

 region. 



It has long been known that the photographic image of a 

 luminous object is dilated at the expense of the dark parts or 

 the field itself. This has been merely attributed to a gradual 

 advance of the chemical action (without further attempt at expla- 

 nation). The phenomenon has recently been studied by M. 

 Angot (Journal de Physique). He finds that the dimension 

 of the images increases with the intensity of the light, with the 

 duration of exposure, with the sensibility of the plate, with 

 diminution of the aperture of the objective, and that it is greater 

 when the plate has not previously been impressed by diffuse 

 light than when it has. M. Angot discards the hypothesis of a 

 mysterious advance of chemical actions, and shows how the 

 phenomena are accounted for by the ordinary theories of optics. 

 This variation of the diameter of images is inevitable in practice ; 

 to render it very small the operator should satisfy himself that 

 the objective used is aplanetic, i.e., free, as far as possible, 

 from aberrations of sphericity and refrangibility. He has only 

 then to take account of variations due to diffraction, which may 

 be attenuated by using objectives of large aperture. It is by 

 using an objective without sensible aberration and of fifteen 

 inches aperture that Mr. Rutherford has succeeded in obtainmg 

 his magnificent photographs of the moon. 



Some interesting experiments on the photo-electricity of 

 fluorspar have recently been described by M. Hankel to the 

 Saxon Academy of Sciences. His attention was drawn to the 

 phenomena in studying the thermo-electric properties of crystals. 

 The new effects were found much more intense than those got 

 by heating the crystal, or by friction of its surface with a brush ; 

 moreover, they were of contrary sign, and«o must be attributed 

 to an action proper to light. Tlae principal results of experiment 

 are these : The centre of a crystalline face presents, after 

 exposure of about an hour to sunlight, a strong negative tension, 

 while the tension towards the sides is much less, and even most 

 frequently positive. An exposure of the crystal to the tem- 

 perature of 95° for several hours produces, during cooling, the 

 smallest positive tensions at all points of the crystal. Experi- 

 ments made by filtering light through coloured glasses, a layer 

 of water, a solution of alum or of sulphate of quinine, showed 

 that the chemical rays are much the most active. Lastly, a 

 too strong concentration of light on the crystalline face removes 

 all sensibility to the ulterior action of light. To give an idea of 

 the degree of tension observed in such experiments, M. Hankel 

 states that a brass plate 95 mm. in diameter, connected with a 

 zinc element, copper, and uninsulated water, gave a deflection 

 (in an electrometer composed of a gold leaf hung from an insu- 

 lated brass rod between two insulated plates of brass) of i°'2 

 on approaching the centre point as nearly as possible, and about 

 o°'6 on approaching the edge. The deflections obtained by 

 exposition to light reached 21", and even 26° in the centre of 

 surface of a crystal electrified by light. 



As supplemental to the article on' the blue gum-tree, at p. 443 

 of Nature, voh xvi., the following notes from a report on the 

 culture of Eucalyptus in Algeria by Consul-General Playfair will, 

 no doubt, be interesting. With regard to rapidity of growth, it 

 seems that the first trees ever planted in Algeria were sown in 

 1862, and upon being measured in 1874, that is at twelve years 



