446 



NATURE 



[Sept. 9, 1880 



4. If June, July, August, or December be warm, the next 

 mmth will probably be a warm one also. 



5. Two months, June and July, tend, when very dry, to be 

 followed by dry ones. On the other hand, a dry August indicates 

 the probability of a wet September. 



6. A wc-t December is apt to be succeeded by a wet January. 

 In addition to the foregoing, there are also a few instances in 



which the rainfall of certain months appears to be definitely 

 related to antecedent extremes of temperature, and vice versa. 

 Thus 



7. If August or .September be warm, the ensuing September 

 or October inclines to be wet. If, on the other hand, September or 

 Kovember be cohl, the succeeding October or December is likely 

 to be a dry month. 



S. If February, June, or July be very dry, the next month has 

 a strong tendency to be warm. 



9. If January, March, or April be wet, we may also expect 

 the next month to be a warm one. But a wet May or July 

 gives a strong probability of cold weather in June or August 

 respectively. 



Mr. W. H. Freece read a paper On the Best Form to give to 

 Lig/itni?!^ Conductors. The question was whether the lightning 

 conductor should be a solid rod, or tubular, or flat. Snow 

 Harris, Prof. Henry, M. de Melsens, and M. Guillemin advo- 

 cated straps of great surface. Faraday strongly maintained that 

 there was no advantage in strap or tube forms, as the surface 

 does nothing in conducting the current. Mr. Preece had 

 ■obtained the use of Dr. De La Rue's magnificent batteries, and 

 had procured conductors of equal material, length, and weight, 

 but differing in form. A condenser charged from 3,400 cells 

 afiforded a very powerful source of electricity, more than forty- 

 two microfarads being thus available to produce an enormous 

 spark. Experiments made by heating and deflagrating wires 

 through the different conductors left no doubt that these dis- 

 ■cliarges do obey the law of Ohm, and therefore that the 

 additional surface of flat and tubular conductors is of no 

 advantage in their conductivity. 



Prof. Osborne Reynolds rather doubted the conclusions of 

 Mr. Preece, on account of our not knowing the conditions under 

 which the electricity passes from the air into the surface of the 

 <:onductor. Prof. Ayrton thought the experiments should be 

 tried with much greater difference of potential. The 3,000 

 •cells would not produce a free spark of more than ^^ of an inch 

 long, whereas flashes of lightning might extend over miles. 



Mr. Preece, in replying, pointed out that increased surface, 

 though increasing its inductive capacity, did not add to its 

 efficiency, which depended only on its conductivity. 



Mr. Preece also communicated an observation on the peculiar 

 behaviour of copper wires. Very powerful discharges of electri- 

 city were found to increase the conductivity of newly-drawn 

 copper wires by an appreciable percentage. Leaden wires 

 showed no such changes. In the subsequent debate it appeared 

 that the opinion was that the effect of the first current was to 

 anneal the wire. 



On the Necessity for a regular Inspection of Lightning Con- 

 ductors, by Richard Anderson, F.C.S., A. Inst. C.E. — The 

 author referred to a paper by M. W. de Fonvielle, "On the 

 Advantage of keeping Records of Physical Phenomena connected 

 with Thunderstorms," read before this Association in 1872. M. 

 -de Fonvielle recommended to the attention of the members the 

 steps which had been taken by the French Government for ob- 

 taining information regarding thunderstorms, and suggested that 

 the Association should institute some organisation for the collec- 

 tion of such data ; arguing that it would be of much value to 

 science, as well as to the public. Nothing, however, has been 

 done by the Association since 1872; and the author not only 

 confirmed the conclusions at which M. de Fonvielle arrived as 

 tO' the desirability of collecting such data, but was of opinion 

 that the organisation should go further, and arrange for a regular 

 inspection of all public buildings which had lightning-conductors 

 applied. 



The necessity for this he demonstrated by adducing a number 

 of striking cases where damage, more or less severe, had occurred 

 to buildings, even though having lightning-conductors attached 

 to them. The cases now cited, he explained, were supplementary 

 to those communicated in his paper on a similar subject to the 

 Asiociation in 1S7S. A few of the cases were as follows :— 



In October, 1S7S, an elevated building situated at the back of 

 Victoria Station, occupied as a furniture repository, was struck 

 by hghtaiug and sustained damage, although furnished with a 



■|-inch by J-inch copper band lightningconductor and a tube of 

 |-inch diameter rising above the iron crestings on the tovver. 

 The lightning shattered the cresting and bent the jioint of the 

 lightning-rod, besides doing other damage to the building. On 

 testing, the author found the resistance very great, and on 

 opening out the earlh-terminal found it imbedded in concrete. 



On June 26 last, lightnmg struck All Saints Church, Lam- 

 beth, doing considerable damage, although there was a f-inch 

 diameter copper-rope conductor on the west gable, with a copper 

 tube rising 18 inches above. A stone cross about 50 feet from 

 the conductor was thrown down, injuring the roof of the north 

 aisle. On testing the conductor, the author found that it had no 

 "earth" whatever, the rope being simply placed in 2 inches of 

 loose rubbish. The copper was of very inferior quality ; con- 

 ductivity being 32'I0 per cent., or about double that of iron. 



The author quoted also a few cases from his recent work on 

 "Lightning-Conductors, their History," &c : — 



In August, 187S, the Powder Magazine at Victoria Colliery, 

 Eurntclijfe, Yorkshire, was strack by ligh'ning, though furnished 

 with a conductor, 13 feet above the building, and terminating in 

 13 feet of clayey soil. The building was blown to pieces. On 

 testing the conductivity of the copper, it was found to be 39"2, 

 instead of 92 to 94 per cent. The conductor was insulated from 

 the building and from a large iron door, which it ought not to 

 have been. 



The author concludes from this evidence that it is not sufficient 

 merely that rods of copper should be attached to a building, but 

 it is necessary that after being fixed they should be regularly 

 inspected, to see if they are in good order, so as to be really 

 efficacious. 



Sir Wm. Thomson gave a communication On a Method of 

 Measuring Contact Electricity. Sir W. Thompson had devised 

 this method at the time when Hankel published his results in 

 1 86 1. A method identical with it had lately been described 

 by M. Pellat, and consisted in employing a small electromotive 

 force in connection with a dividing resistance slide, to give a 

 counterbalancing electromotive force to that produced by contact. 



Sir W. Thomson next described A Method of Determining 

 -without Mechanism the limiting Steam-Liquid Temperature of 

 a Fluid. This was a simple apparatus, consisting of a closed 

 glass tube containing liquid sulphurous acid filled to a suflicient 

 height to insure that the liquid in the lower half will expand to 

 the top. Prof. W. Ramsay criticised the proposal, and stated 

 that he had found an a;iparatus in which a screw was employed 

 to produce increase of pressure instead of using the expansion 

 of the liquid itself. With this apparatus he had repeated 

 Andrews' research on a large number of substances. 



Mr. G. F. Fitzgerald read a paper On the Possibility of origi- 

 nating Wave-disturbances in the Ether. This was a mathemati- 

 cal paper, in which, by comraring the equations of Maxwell's 

 theory of the propagation of electric action through a medium 

 with those of direct action at a distance, he deduced the conclu- 

 sion that electric currents and systems cannot originate in the 

 ether such disturbances as those of light. 



Mr. R. M. Shida gave an account of A Nnv Determination of 

 the number of Electrostatic Units in the Electromagnetic Unit. 

 The value V of this ratio he deduced was 294-4 X 10'. 



M. Wilfrid de Fonvielle exhibited his magnetro-electric gyro- 

 scope, which has been already described in our pages. 



M. Jansen sent a communication to the Section, which was 

 read by the Secretary, upon his recent researches On the obtain- 

 ing Positive Photographs by Prolonged Exposure. 



Mr. Wiesendanger showed a new electromotor, which will be 

 described hereafter in our pages. 



Mr. Philip Braham exhibited an ingenious adaptation of lime- 

 light for microscopic illumination, and also described a simple 

 instrument for detecting polarised light. 



On the Best Form of Magnet for Magneto Machines, by W. 

 Ladd. — At the British Association meeting at Dundee in 1867, I 

 made some remarks upon different forms of magnets, and exhibited 

 these diagrams, showing, by the "lines of force" naturally 

 arranged, the great superiority of the circular magnet where an 

 armature is to be employed. 



Since that time some thousands of that form of magnet have 

 been made for medical, mining, and other purposes. 



Some months ag-i, in conversation with M. Bregnet of Paris, 

 I showed him these same diagrams, and he was very much 

 impre-sed with their importance ; he has since then constructed 

 a machine, using the Gramme armature, and with a smaller 

 quantity of steelm the magnets he has made a far more powerful 



