6l2 



NA TURE 



[April 26. 1900 



sea-level. Furthermore, according to the theory of driven 

 cyclones, the progressive motion of the cyclone is supposed to 

 be determined by the " prevailing west component " of the 

 upper currents. At Blue Hill the mean westerly component of 

 the upper current is 35 metres per second at 9000 metres, 

 about 17 metres per second at 4000 metres, and i metre per 

 second at 200 metres (//rt/^az-rt^ Observatory Annals, 1890, vol. 

 xl. p. 447). It is natural to suppose that a driven whirl, in such 

 conditions, would be rapidly toppled over and destroyed. Yet 

 storms persist for days. If, however, a driven whirl did persist 

 in such conditions, its axis if lilted at all would, according to all 

 analogy, be tilted in the direction of progressive motion. Yet 

 the direct observations with kites at Blue Hill, and the observ- 

 ations of clouds by Ley in England, prove that the axis of the 

 cyclone is tilted backward. Moreover, it is reasonable to sup- 

 pose that the air in the rear of a driven whirl would partake of 

 the progressive motion of the whirl, and this, added to the in- 

 draught, would make the wind velocity in the rear of the whirl 

 very much greater than that of the winds in front, yet such is 

 not generally found to be the case. For these reasons I think 

 the observations do not favour the theory of driven cyclones. 



The theory of cyclones with which the observations in tem- 

 perate latitudes seem best to agree, is the theory which supposes 

 the cyclone to result from contrast of temperature in a horizontal 

 direction. This I have called the convection theory. In this 

 theory there are two types of cyclone. The warm-centre cyclone 

 of the lower atmosphere, and the cold-centre cyclone of the 

 upper atmosphere. The best type of the cold-centre cyclone is 

 the polar cyclone ; but there also exist in the upper air in tem- 

 perate latitudes small travelling cyclones or //^w /-cyclones of the 

 same nature. Horizontal contrasts of temperature are most 

 marked in winter, hence the theory explains why cyclones are 

 most violent in winter. The origin of the horizontal contrasts 

 of temperature is not shown by observation. They probably 

 arise by the interchange of air between higher and lower lati- 

 tudes. A body of air moving from the equator toward high 

 latitudes would come into a region where it would be nearly 

 surrounded by colder air, and the conditions would favour the 

 production of a warm-centre cyclone. A body of air moving 

 toward the equator would produce conditions favourable to a 

 cold -centre cyclone. H. H. Clayton. 



Blue Hill Meteorological Observatory, March 30. 



Rcck-structures in the Isle of Man and in South Tyrol. 



If the intercrossing of two separate systems of folding be the 

 essential condition in the complicated rock-structures so ably 

 worked out by Mrs. M. M. Ogilvie Gordon in South Tyrol, I 

 scarcely think the parallelism with the conditions in the Manx 

 Carboniferous rocks can be so close as Mrs. Gordon suggests in 

 her recent letter (Nature, March 22, p. 490). 



So far as I have been able to judge, the disturbances in the 

 Carboniferous volcanic rocks of the Isle of Man were the result 

 of a movement which was single both as regards direction and 

 time. It is true that this conclusion was reached in 1897, 

 before Mrs. Gordon had taught us the importance of torsion- 

 structure in areas of disturbance ; but I re-examined the sections 

 last autumn, after having studied Mrs. Gordon's paper, without 

 finding any reason to alter my former opinion on this point. 

 The interpretation given in my recent paper {Q.J.G.S. vol. 

 Ivi. p. 1 1 ) is therefore in all respects the same as that published 

 in brief in the official Summary of Progress of the Geological 

 Survey for 1897 (pp. 110-112). 



It seems necessary, also, to call attention to the small scale 

 of the structures in question in the Manx Carboniferous rocks. 

 Their most striking feature is their sudden local development 

 in a limited tract where the strata are rendered by diverse 

 lithological composition peculiarly susceptible to differential 

 displacement. Under such conditions, it appears that even a 

 small degree of lateral movement may be so focussed as to 

 cause great disturbance at certain places without much disturb- 

 ance of adjacent tracts. The post-Carboniferous movement in 

 the Isle of Man can scarcely have been even approximately of 

 the magnitude of the disturbances in South Tyrol described by 

 Mrs. Gordon. 



It was in pre-Carboniferous times that the Manx region 

 underwent earth-movements of really grand intensity ; and Mrs. 

 Gordon may have had this fact in mind in referring to the 

 subject. In the Older Palaeozoic (probably Cambrian) slate- 

 rocks of the island, " crush-conglomerate" has been developed 



NO. I 59 I, VOL. 61] 



on a very extensive scale by differential shearing, as described 

 by Prof. W. W. Watts and myself five years ago {Q.J.G.S. 

 vol. li. p. 563). These rocks, moreover, show evidence of succes- 

 sive epochs of disturbance, varying slightly in direction but ap- 

 parently all pre Carboniferous. The production of the " crush- 

 conglomerate " appears to have occurred during only one of 

 these stages. It is not improbable that an observer acquainted 

 with the "torsion-structures" of the Dolomites might be able 

 to find parallel phenomena among the highly complicated 

 pressure-structures in the Manx Slates ; but I think that a sharp 

 distinction should be drawn between these structures and those 

 of the Carboniferous rocks of the island. G. W. Lamplugh. 

 Tonbridge, April 8. 



Electric Light Wires and Dust. 



I BELIEVE that the collection of dust upon electric light wires 

 and fittings is generally attributed to air currents, due to ther- 

 mal causes, the same thing occurring, to some extent, with hot- 

 water pipes. Recent experience has, however, convinced me 

 that in the case of electric light conductors, electrostatic attrac- 

 tion is really the chief factor, particularly where the supply is at 

 200 volts from the street mains. In my office here I have 

 several electric light cords strung across the ceiling. They are 

 all exactly similar and under the same conditions, except that 

 some of them have the switch in the negative and some in the 

 positive conductor. The former gather dust to an extraordinary 

 degree, and now, after a few months' use, have become quite 

 an eyesore. The latter are practically as clean as when first 

 put up. As is well known, the negative conductor of a street 

 supply tends always to earth itself, and, as a matter of fact, in 

 my case I find that the negative of my supply from the West- 

 minster Co. is almost at earth potential. The positive, on the 

 other hand, is nearly 200 volts above the potential of the earth. 

 In this lies obviously the cause of the phenomenon. The wires 

 which have the switch in the negative are nearly at 200 volts 

 potential above the earth whenever the switch is off, while those 

 which have the switch in the positive are at zero potential in 

 these circumstances. Of course, when the switches are on, all 

 the cords are under similar conditions, one conductor in each 

 being nearly at 200 volts above earth, and the other at about 

 earth potential. No doubt it is when the switch is off, in the 

 case where it is in the negative conductor, that the accumula- 

 tion of dust takes place. Having regard to the comparative 

 lowness of the 200 volts potential, from an electrostatic point 

 of view, the rate at which the dust accumulates on the cords is 

 most surprising, and this is my reason for thinking it worth 

 while bringing the matter to notice. A. A. C. SwiNTON. 



66 Victoria Street, Westminster, April 23. 



ON THE SIZE AT WHICH HEAT MOVE- 

 MENTS ARE MANIFESTED IN MATTER. 



IN the molecular theory of heat it is assumed that the 

 motions of atoms and molecules are the motions 

 upon which the phenomena of temperature depend. 

 These motions are assumed to be very irregular, and the 

 apparent uniformity of structure of a gas, for example, 

 is attributed to the very small size and irregularity of the 

 motions, which within any region of sensible size are the 

 same, on the average, as within any neighbouring region. 

 Within regions of molecular dimensions the distribution 

 of motion is extremely irregular ; neighbouring molecules 

 are not in general moving at the same speed or possibly 

 vibrating in the same way. Hence in this view the size 

 at which heat movements are manifested in matter are 

 of molecular sizes, i.e. from io~'' to lo"* cm. 



In addition, however, to all this matter, motion and 

 vibration, there are present ether motions of an irregular 

 kind. Within any closed envelope at constant tempera- 

 ture the ether motions must be in statistical equilibrium 

 with the motions in the envelope. The energy per c.c. 

 of these ether motions will be considerable at high tem- 

 peratures, and small at low ones. Many years ago I 

 called attention to the energy per c.c. required in order 

 to, in this sense, warm up ether, and showed that it was 

 quite comparable with that required to warm up a rare 



