574 



NATURE 



[April 13, 1893 



Mr. S. J. Dickson, says, " From the 9th to the 13th of October, 

 he weather was unusually oppressive with threatening storms, 

 and on the evening of the 1 3th a heavy storm was seen to be work- 

 ing up from the west accompanied by incessant lightning of every 

 description, and about 8 p.m. it broke over the homestead in all 

 its fury, the wind was from south-west and of terrific force, and 

 the rain and hail were very severe. The hailstones were as large 

 as hen-eggs, and in some of the paddocks, one particularly, it 

 pounded the herbage completely out, so that not a vestige of it 

 was left, although before the storm came on it was from six to 

 twelve inches high, and in other places strong variegated thistles 

 three to four feet high were beaten down. Trees some two feet 

 thick, that the wind could not tear up by the roots, were snapped 

 off short as if made of matchwood. In the storm the hail killed 

 birds innumerable, and even domestic fowls roosting on the trees 

 were killed by it, and after the storm a large snake was found 

 cut into two pieces by the hail, so at least it appeared. On the 

 open plain the hail laid four to six inches deep, and the whole 

 country looked as if a heavy snowstorm had passed over it. Trees 

 in the track of the hail were completely denuded of leaves, and the 

 bark knocked off tree trunks and limbs. The storm wind carried 

 away outstations, unroofed the hayshed, damaged the woolshed, 

 and carried away two sides of the house-verandah, and the sheets 

 of iron from it were found nearly half a mile (30 chains) away to 

 the north-east, round wall plates in the hayshed six to eight inches 

 thick were broken to pieces, and the iron roofing on all the build- 

 ings was battered by the hail as if some one had pounded it with 

 a hammer all over. The storm track was only a mile to a mile 

 and a half wide, at least the hail part. Between 7 and 8 p.m., 

 as the storm came up, there seemed to be a white bow in the 

 sky, like a white rainbow stretching from north to south. I 

 have seen heavy storms before, but I never wish to see another 

 like this. The shearers were completely terrified, and all say 

 that they have never experienced a storm like it, in fact, it 

 beggars description and can hardly be realised. It was an 

 experience that we shall remember as long as we live." 



North of Narrabri, and especially between Narrabri and 

 Avondale, the storms were very severe. Midway between these 

 places and at Terry-hi-hi and Berrigal Creek the wind worked 

 great destruction in the forest. How violent it was may be 

 gathered from the fact that great trees twelve feet in circum- 

 ference at three feet from the ground, were snapped off short 

 ten feet above the ground, or entirely stripped of their limbs. 



SCIENTIFIC SERIAL. 

 American Meteorological Journal, March. — Exploration of 

 the free air, by Prof. M. W. Harrington. The author considers 

 that the conclusions to be drawn from weather maps are nearly 

 exhausted, and that the reason of the imperfection of meteoro- 

 logy is the want of knowledge of what is going on in the free 

 air. Mountain observations give most important results, but 

 they are still surface observations. We know what goes on at 

 the base of a cyclone, but not what occurs at the top. Theories 

 • are deduced from cloud observations, but we lack actual know- 

 ledge of what is going on above, and the only means available 

 at present is systematic balloon observations. Prof. Harrington 

 thinks that such observations should be provided for by funds 

 from private sources. — The general winds of the Atlantic Ocean, 

 by Prof. W. M. Davis. The basis of this discussion is the 

 "Sailing Directory of the Atlantic Ocean," published by the 

 Deutsche Seewarte, and especially two generalised wind charts 

 contained in the atlas accompanying that work. The author classi- 

 fies the winds as planetary (due to the earth's rotation and the 

 influence of the sun), terrestrial (the annual migration of the 

 wind belts north and south, and the seasonal variations of 

 velocity and direction), including the interruptions of continents 

 and mountain ranges. — The colours of cloudy condensation, by 

 Prof. C. Barus. The author considers the problems connected 

 with the condensation of water from moist air,. and reviews the 

 labours of Mr. Aitken and Mr. Bidwell with reference to the 

 particles of an opaque steam-jet. He also gives a minute de- 

 scription of the apparatus employed in his own investigations. 



SOCIETIES AND ACADEMIES. 



London. 



Physical Society, March 24.— Prof. A. W. Rucker, F.R.S., 



President, in the chair. — Several excellent photographs of flying 



bullets and of the air waves produced by vibrating hammers, 



NO. 1224, VOL. 47] 



were exhihjted, the originals of which had been taken by Prof. 

 Mach. — A paper on the differential equation of electric flow was 

 read by Mr. T. H. Blakesley. The object of the paper is to 

 show that the ordinary mathematical expressions for electric 

 flow fail to explain all known facts, and to point out that in 

 order to interpret these facts certain properties of matter not 

 usually recognised must be admitted. The subject is treated 

 both algebraically and geometrically, in the latter case the 

 magnitudes being represented by the projections of the sides of 

 a triangle revolving in its own plane on a fixed line in that plane. 

 Taking the ordinary differential equation for a simple circuit 



having resistance and self-induction, viz.,V- L"^ = RC, it is 

 shown that this takes no account of any energy except that 

 spent in heating the conductor, and that where radiation into 

 space is concerned, it is necessary to introduce another term AC, 

 where A is a quantity of the nature of resistance. It is further 

 pointed out that if work be done outside the circuit, the line 

 which geometrically represents the induced E.M.F. cannot be 

 perpendicular to that indicating the current and "effective" 

 E.M.F., the latter term being defined to mean the value of the 

 quantity which is numerically equal to theproduct of the current 

 into the resistance. A magnetic phase-lag must therefore exist. 

 The author also shows that a magnetic field induced in phase 

 with the magnetic induction would not result in a loss of energy, 

 and no hysteresis could exist. Under the same circumstances 

 there could be no radiation of energy from an alternating 

 magnet. A Leyden jar discharging through a circuit having 

 self-induction is next considered. Taking the ordinary premises, 

 it is shown that no provision is there made for energy radiated 

 into space, and tJiat magnetic lag is necessary for the existence 

 of such phenomena. The differential equations for the variables 

 in condenser discharges according to ordinary assumptions are 

 shown to be of the same form, and the variables can be repre- 

 sented by the projection of the sides of a triangle which is 

 simultaneously undergoing' uniform rotation and linear logar- 

 ithmic shrinking. The rate of shrinking is the same as that of 

 the radius vector of an equiangular spiral of characteristic angle j3, 

 /K R 



where cosjS 



V L' 



K, L, and R representmg capacity. 



self-induction, and resistance respectively. The equations and 

 their consequences are considered at some length, and several 

 important properties brought out. To allow for radiated energy, 

 R must be virtually increased from R to R -h A, and the total 

 energy is divided between the circuit and the field in the ratio of 

 R to A. If, therefore, the circumstances be such that A is large 

 compared with R, say by having high frequency, the heating of 

 the circuit may only be a small part of the total energy. In 

 this direction the author thinks the true explanation of some of 

 Tesla's experiments is to be found, the energy being expended 

 chiefly in radiation and not in current through the experimenter's 

 body. Prof. Perry thought the C-R term would not represent 

 the heating of the wire when the oscillations were rapid, owing 

 to the distribution of current not being uniform over the 

 section of the conductor. Maxwell had shown that certain 

 throttling terms had to be considered. In condenser 

 discharges the complete equation would have many terms. 

 Prof. O. J. Lodge said the best definition of R in such case, 

 was that derived from Joule's law rather than that of Ohms 

 Frequency was very important in the radiation of energy, but 

 even at ordinary frequencies of alternators some energy was 

 radiated. Referring to Tesla's experiments, he said the reason 

 why no serious consequences followed, was that there was not 

 much energy behind them. High frequency might be instru- 

 mental in preventing injury, but this he thought remained to be 

 proved. Dr. Sumpner pointed out that losses other than C^R 

 (R being the ordinary resistance of the conductor) had to be 

 taken into account. In some cases, such as transformers on 

 open circuit, the effective resistance might be loco times that 

 of the coil. To discuss completely the problem taken up by 

 Mr. Blakesley, it would be necessary to take account of non- 

 uniform distribution of current, both across and along the 

 conductor, as well as the character of the magnetic and electiic 

 fields surrounding the circuit. Mr. Swinburne thought there 

 was a tendency to over-estimate the rate of high-frequency 

 currents, for unless the coils of transformers were as-umed 

 geometrically coincident, calculations were difficult. Errors of 

 hundreds per cent, were quite possible. In Tesla's experiments 

 no great power was involved, for the transformer could not 

 give out any large power. Mr. Blakesley, in reply, said the 



