i6o 



NA TURE 



[June 1 6, 1887 



There are four factors affecting the lightning-danger to buildings ; 

 two physical — unequal frequency of storms, and geological 

 character ; and two social — variable population, and mode of 

 building. Of all trees, oaks are most frequently damaged, 

 beeches most rarely (in the ratio 54 to i). 



An electric trumpet has been recently devised by M. Zigang 

 {La Nature, June 4). It consists of a short brass tube mounted 

 on wood and containing ah electro-magnet whose ends face a 

 vibrating plate, on which is fixed a small piece of soft iron. 

 Against this plate-armature rests a regulating screw with 

 platinum point, which serves for automatic interruption, by 

 vibration of the armature. With two Leclanche elements a 

 musical sound is had, which may be varied in pitch, intensity, 

 and timbre by means of the screw. This instrument may be 

 usefully employed in signalling on ships, railways, tramways, &c. ; 

 it may also serve as a receiver for signals of the Morse type. 



Prof. Christensen, of Copenhagen, has recently {Journal 

 fiir praktische Chemie, 1887, No. Ii) made a redetermination of 

 the atomic weight of fluorine, with the satisfactory result that 

 this element is to be added to the already large list of those 

 whose atomic weights are whole numbers and simple multiples 

 of that of hydrogen. The determination was based upon the 

 analysis of a double fluoride of ammonia and manganese, 

 4NH4F . Mn2F6, the extreme precautions displayed in the pre- 

 paration and purification of which show the peculiar difficulties 

 attending work upon this singular element. It is very interest- 

 ing to read of the filtrations through platinum gauze placed in 

 gutta-percha funnels, of the drying of the beautifully crystalline 

 red salt sj^read out upon wide expanses of platinum-foil, and of 

 the skilful manner in which all traces of silicon were eventually 

 eliminated. The results of the numerous analyses show that, if 

 Stas's value for oxygen be taken as the standard, the atomic 

 weight of fluorine is 18 '94, but if, as Mendelejeff concludes, 

 oxygen be 16, then the atomic weight of fluorine becomes iS'gg, 

 or, in round numbers, i9"o. 



It will probably be remembered that, early in the year 1 883 

 {.Ber. der Dezct. Chem. Ges., xvi. 324), a number of chemical 

 reactions, especially the formation of arseriides from mixtures of 

 metals and arsenic, were brought about, by Dr. W. Spring, by 

 subjecting the powdered mixtures to the immense pressure of 

 6000 atmospheres. A still more striking experiment, entirely 

 unique in its way, has just been made by Dr. Spring, in con- 

 junction with Dr. Van't Hoff {Zeitschrijt fiir physikalische 

 Chemie, i. 5). In the course of a study of chemical dynamics 

 these workers found that the blue-coloured double acetate of 

 copper and calcium, (C2H302)4CaCu . 8H3O, is perfectly stable 

 at atmospheric pressure as far as 75° ; above this temperature it 

 is decomposed into its constituent acetates, three-quarters of its 

 water of crystallization being set free. This decomposition is 

 atended with contraction in volume, and the salts dissolve in the 

 liberated water. The idea was at once suggested. Could this 

 decomposition be effected by means of Dr. Spring's powerful 

 compressing machinery ? The idea was carried out, and no 

 sooner was the pressure upon the solid double acetate increased 

 to 7000 atmospheres, at a temperature of 40°, than the solution 

 of the separated constituent salts spurted from every joint of the 

 apparatus, and on releasing the pressure the resolidified mass 

 was found to consist of a mixture of the white calcium and the 

 green copper salt. 



Last week we referred to the fact that the Council of the 

 Meteorological Society are anxious to obtain photographs of 

 flashes of lightning. The Photographic News, dealing with the 

 conditions under which such photographs should be taken, notes 

 the following points as imjjortant : — "First, the exact position 

 of the camera. In many countries, ordnance maps can be ob- 

 tained on such a scale that a minute dot will indicate the position 



of the camera within a foot or two, and it will often be easy to 

 record the position of the apparatus with far greater exactness, 

 as, for example, when the camera is placed at a window. A 

 thread with a plummet should be allowed to range from the 

 optical centre (say the diaphragm in case of a doublet) to the 

 floor, where a mark should be made. Second, the time at which 

 the exposure was made. Third, the aspect of the camera. 

 When the locality is exactly recorded, this datum may be ap- 

 proximate, as there will generally be the means of exactly deter- 

 mining it upon the plate itself. Fourth, the equivalent focus of 

 the lens, but the determination of this may well be left until it 

 it is found that something valuable may be deduced from the 

 photograph. Fifth, the distance of the flash. The recording 

 of this is a very important matter, as, when the focus of the lens 

 is known, it will be easy to determine the actual distance 

 between cloud and earth, also the horizontal angle subtended to 

 the observer at the camera. To determine the distance, the 

 observer should note as accurately as possible the time elapsing 

 between the flash and the report, and in doing this, even such a 

 chronograph watch as may now be had for five or six pounds will 

 be found of great service." 



At a meeting of the Middlesex Natural History and Science 

 Society, at the Natural History Museum, South Kensington, on 

 the nth inst.. Prof W. H. Flower, F.R.S., gave an address on 

 the teeth of the Mammaha, especially referring to those speci- 

 mens exhibited in the case in the Index Museum. Details of 

 the structure, growth, and disposition of the teeth in the jaw 

 were given, and the peculiarities of vestigial and rudimentary 

 teeth pointed out. Prof. Flower referred to the value of these 

 index museums, calling special attention to that of mineralogy, 

 arranged by Mr. Lazarus Fletcher, and which for greater con- 

 venience was placed in the mineral gallery. 



This evening, Prof A. W. Williamson will deliver an address, 

 in the Chemical Theatre, to the London University College 

 Chemical and Physical Society. He has chosen as his subject, 

 "Atomic Motion." Sir Henry Roscoe will take the chair. 



" My Microscope, and Some Objects from My Cabinet," a 

 simple introduction to the study of " the infinitely little," by a 

 Quekett Club man, is announced for immediate publication by 

 Messrs. Roper and Drowley. The little volume is dedicated to 

 the President and Members of the Quekett Microscopical Club. 



Messrs. Whittaker and Co. will publish early next week 

 Mr. E. C. Robin's book on "The Design and Construction of 

 Applied Science and Art Buildings, and their Suitable Fittings 

 and Sanitation." 



The Thuringian Fisheries Union held their tenth meeting at 

 Jena on May 26. One of the members stated that 64,000 young 

 salmon had been placed in the Saale last year. The Grand 

 Duke of Saxe- Weimar was present at the meeting, and took 

 part in the debates. 



Dr. Moritz Wagner, Professor at the Munich University, 

 died at Munich on May 31. He was well known as a scientific 

 traveller, and author of some excellent works of travel. 



During the five months ended May 1887 the total value of 

 the fish landed on the east coast of Scotland was ;i^335,366 ; on 

 the west coast, ;!{r7S,290 ; in Orkney and Shetland, ^34,516; 

 the total value for five months being ;^445, 1 72. As compared 

 with the corresponding period of last year, this was a decrease 

 of ;^4, 113. The last month, however, showed an increase of 

 ;^6,478 over the corresponding month of the year 1886. 



Artificial clouds for the protection of vines from frost were 



produced in a vineyard at Pagny on the Franco-German frontier 



during the night of May 13. About 3 a.m., when the thermo- 



j meter had gone down to - i°'5 C, the signal was given to ignite 



