August 23, 1888J 



NATURE 



393 



apart, and we shall then observe the time which an 

 electromotive impulse communicated at one end takes to 

 travel to the other. Instead of using two wires, we may 

 if we like use what comes to much the same thing, viz. a 

 single wire suspended at a reasonable height above the 

 ground, as in a common land telegraph. Such a case as 

 this is much the same as if two wires were used at a 

 distance apart equal to about twice the height above the 

 ground. 



The experiment, if it could be accurately made, would 

 result in the observation of a speed of propagation equal 

 to 3 x io 10 centimetres per second. The actual speed in 

 practice may be less than this, by reason of the various 

 circumstances mentioned, but it can never be greater. 

 This, then, is the rate of transmission of transverse im- 

 pulses, and therefore of transverse waves, through ether 

 as free as it can be easily obtained. 



There are many methods known to physicists by which 

 an indirect experimental determination of this velocity 

 can be made. These methods are more easily practicable 

 than the one described : they directly determine the 

 ratio kin, or, what is the same thing, the product K/X, and 

 .it is left to theory to say that this is really the velocity of 

 .electrical pulses in free ether. It is unnecessary to say 

 more about them here. Oliver J. Lodge. 



( To be continued)) 



A HISTORY OF THE AUGUST METEORS. 



THE August meteor-shower has been more frequently 

 -*■ observed than any other with which we are 

 acquainted, and the modern history of this remarkable 

 system includes many interesting circumstances. It has 

 not, in recent times, given us displays equal in grandeur 

 to periodical swarms like the Leonids of November 13 

 and Andromedes of November 27, being decidedly less 

 rich in point of numbers. But what this stream lacks in 

 this respect is compensated for by the annual visibility of 

 the shower and by the intense brilliancy of some of its indi- 

 vidual members. Every year the August meteors present 

 a conspicuous appearance on the night following St. 

 Lawrence's Day, and fire-balls of excessive lustre are now 

 and then interspersed with the smallest perceptible 

 shooting-stars of the system. The Leonids and Andro- 

 medes, which have rendered the month of November so 

 famous in meteoric annals, can only reappear abundantly 

 at intervals of thirty-three and (probably) thirteen years, 

 whereas the Perseids of August are unfailing in their 

 .regular apparitions as the epoch comes round each year. 

 On the night of the 10th the most casual observer will not 

 fail to notice the surprising frequency of shooting-stars, 

 and must remark their occasional brilliancy and the per- 

 sistency of the phosphorescent after-glows which they 

 generate during their rapid flights amongst the fixed stars. 



The early history of the August meteors is vague and 

 meagre in the extreme. Ancient writings are significantly 

 mute as to the scientific aspect of meteor-showers. 

 Doubtless in olden times these phenomena were equally 

 as plentiful as at present, but amid the ignorance and 

 superstition which prevailed they were little regarded. 

 The prominent part which meteors play in the solar 

 system was not suspected, hence no importance was 

 attached to their appearance. They were supposed to be 

 mere exhalations uncontrolled by fixed laws, and it is 

 entirely due to modern science that their true character 

 has been revealed, and that they have been raised to the 

 dignity of bodies having a celestial origin, and probably 

 also an extensive influence throughout the wide range of 

 astronomical physics. 



But former records, if void of particulars possessing a 

 scientific utility, are yet often useful in supplying dates. 

 Many old references to meteor-showers, though very im- 

 perfect in description, are, by the accordance of epoch, 

 justly assumed to have been early exhibitions of the very 



same systems as those which have furnished some of the 

 most imposing displays of recent years. In the catalogue 

 of 315 meteoric showers compiled by Quetelet, a consider- 

 able proportion are probably identical with the August 

 Perseids, and below we give the dates, up to a century 

 ago, of these : — 



The dates in the ninth and tenth centuries are some- 

 what different from those in later years, but this does not 

 negative the assumed relation, because they are brought 

 nearly into agreement when the change of style in 1752 is 

 allowed for. This proves the showers to have really 

 occurred at a period early in August according to present 

 reckoning. There may also be a slight alteration in the 

 epoch of the swarm due to a shifting of the node, which, 

 in its cumulative amount after many ages, might reach a 

 considerable value. For the reasons assigned, the cele- 

 brated shower of Leonids which now takes place on 

 November 13 was observed in October 902, and again on 

 October 19, 1202, October 22, 1366, &c. 



Muschenbroek, in 1762, announced the general fact 

 that he had observed shooting-stars to be more plentiful 

 in August than in any other month of the year. Further 

 towards the close of the century this was in part confirmed 

 by the apparition of many meteors on August 8 and 9. 

 In 1806 and 1812, Dr. Forster, of Clapton, recorded in 

 his ' ; Calendar " that these phenomena were unusually 

 abundant on August 10, and in the latter year he particu- 

 larly noted the extraordinary length and phosphorescent 

 aspect of the trains left in their wake. Subsequently the 

 same epoch was amply corroborated ; and in 1835, 

 Quetelet definitely mentioned the 9th and 10th of August 

 as the date of maximum annual display. 



On August 9, 1837, M. Wartman, of Geneva, observed 

 82 of these meteors between 9 p.m. and midnight. In the 

 following year, on August 10, observations were made at 

 Geneva and at Planchettes, a village 62 miles north-east 

 of Geneva, with the view of determining the heights and 

 velocities of the meteors. A discussion of the results 

 showed that the average elevation above the ground was 

 550 miles, and the velocity 220 miles, but these figures 

 are now known to have been enormously in excess of the 

 true values. 



From 20 meteors observed in August 1863, Prof. A. S. 

 Herschel determined the mean height as 8r6 miles at 

 first appearance and 577 miles at disappearance, and the 

 velocity was found to be 34*4 miles per second. From 27 

 meteors similarly observed in Italy between August 5 and 

 10, 1864, Secchi derived limiting heights of 766 and 497 

 miles ; and, averaging these with the results obtained by 

 Prof. Herschel in the preceding year, we get 78 to 54 

 miles, which may be adopted as representative values for 

 the normal heights not only of the Perseids, but of 

 shooting-stars generally. 



Heis, Schmidt, Greg, and Herschel were amongst the 

 first to methodically observe the August meteor-shower 

 and determine its radiant point in the northern region of 

 Perseus. In 1863, August 10, an unusual display was 

 witnessed, for on this occasion the stream seems to have 

 attained a degree of intensity not recorded either before 

 or subsequently to that year. In 1871 there was also 

 a very pronounced and abundant appearance of these 

 meteors. In Nature, vol. xx. p. 457 (September 11, 

 1879), will be found some details as to the relative number 

 of August meteors counted in different years. 



