6o6 



NA TURE 



[April 2?>, 1887 



Clausius, than whom none could be a more unprejudiced witness. 

 "At the same time in the theoretical development of the 

 mechanical theory of heat, in which the relation between 

 heat and work often occurs, the method of expressing heat in 

 mechanical units effects such important simplifications that the 

 author has felt himself bound to drop his former objections to 

 the method on the occasion of the present more connected 

 exposition of that theory." Archd. C. Elliott 



Edinburgh, April 18 



Seismometers 



I HA's'E long ago learnt not to look for any fair recognition 

 of my work in seismometry on the part of Prof. John Milne, 

 and when he accuses me of appropriating without acknowledg- 

 ment the work of others it is time to decline further controversy 

 wiih him. The points raised in his last communication (Nature, 

 April 14, p. 559) aresufiSciently answered in mine of December II 

 (p. 172). I there quoted part of a letter written by Prof. Chaplin, 

 now of Harvard University, then of Tokio, and Secretary of 

 tlie Seismological Society of Japan, under whose eyes the events 

 occurred to which Prof. Milne refers. I did not quote the whole 

 of Prof. Chaplin's letter, because it contained sentences I was 

 unwilling to give except under the strongest provocation. After 

 referring to my seismograph in the words already quoted (p, 172), 

 Prof. Chaplin continues : — 



"I do not remember that in the discussions on your machine 

 Mr. Gray ever claimed to have invented a similar machine, 

 and I am surprised to know that he makes that claim now. On 

 this and other points it appears to me that Messrs. Gr.iy and 

 Milne have not treated your inventions and investigations with 

 fairness, and that you have just grounds for complaint. I am 

 willing you should make such use of this note as you see fit." 



As to the question of priority, this judgment, from a man at 

 once unprejudiced, most competent to form an opinion, and 

 fully informed of the matter in dispute, must (so far as I am 

 concerned) close a discussion of which your readers cannot but 

 be weary. With your permission I shall give, in a later number 

 of Nature, an example of the excellent work which Prof. 

 Sekiya is now doing with my instruments in Japan. 



J. A. EVVING 



University College, Dundee, April 16 



April Meteors 



The Lyrids have, this year, offered a somewhat scanty display, 

 though a few brilliant meteors have been seen shooting from the 

 usual radiant-point. 



In 1SS4 April 19, this shower was very rich, the horary num- 

 ber of its meteors for one observer being .about 22, but in the 

 following year, 1885, it exhibited a considerable decline, the 

 hourly rate being only 3. In 1 886 I obtained no observations, 

 owing to the bright moonlight and in the present year, on April 

 20, the horary number was slightly more than 2, so that the 

 numerical character of the recent display has fallen far short of 

 some of its apparitions in preceding ye.ars. 



On the night of April 17, this year, the shower Imd not visibly 

 opened, for none of its meteors were recorded in a 2J hours' 

 watch. On each of the nights of the i8th and 19th the sky was 

 closely observed for 4J hours, but the Lyrid shower was very 

 feeble, and only furnished i meteor per hour. On the 20th, in 

 3 hours I noted 7 Lyrids, and these were brilliant. 



The aver.age r.adiant-point from the three nights was at 

 269° + 32°, and there is confirmation that this point .advances 

 in R.A. with the time, though not to the marked degree 

 ascribed in Nature for May 7, 1S85, p. 5. But the meteors 

 from this stream have been so scarce at their late recurrence that 

 it has been very difficult to ascertain the exact radiant for each 

 night. Moreover, these Lyrids move with great apparent 

 velocity, flashing out with extreme suddenness and they are 

 gone, together with the faint streaks so netimes accompanying 

 theoi, before the eye is enabled to catch the direclio.is with 

 satisfactory precision. 



On the four nights April 17 to 20 inclusive, I noticed 70 

 shooting-stars belonging to the minor systems of the Lyrid 

 meteoric epoch, and amongst these the best was that of a radiant 

 of very swift, short meteors at 231° -h 17°, a few degrees west of 

 ^ Serpentis. This stream is-not new, for I saw a well-defined 

 shower of Serpentids from the same point during my observa- 



tions of the Lyrids in 1885, on April 19-20 (Nature, May 7, 

 1885, p. 6). 



In this and in previous years I have also recorded some 

 meteors ascending in very long flights from a radiant centre 

 close to 8 Libra;, at 235°— 15°. This is the only observation of 

 this shower at the April period, though Lieut. -Colonel Tupman 

 found a pair of radiants near the position assigned in the first 

 week of March 1869-70. 



I subjoin a short list of bright meteors seen here while watch- 

 ing the progress of the Lyrids, and I should be glad to hear that 

 any of these had been observed elsewhere. 



Date Hour Mag. 



13 46 

 9 4S 

 10 29J 



Bristol, April 22 



Apparent Path 

 Fro:n To 



Notes Radiant 



243 + 14 

 239 + S3 

 308 + 40 



269 -f- 1 Swift, streak 

 56 + 65J Swift, streak 



114 — 4 Very swift 



Swift, streak 

 Slow, train 

 Very sw.ft 



234 -I- 5 

 269 4- 62 

 SiO + 40 



Lyrid 

 279° +. 13° 



Lyrid 

 206° -t- 1 8' 



W. F. Denning 



Vertical Decrement of Temperature and Pressure 

 In Nature of March 10 (p. 437), Mr. Maxwell Mall gives an 

 interesting table of the vertical distribution of temperature and 

 pressure in Jamaica, and, apparently in happy ignorance of 

 the d.angers of the process known as extr.apoIation, goes on to 

 apply the results of observations extending to a maximum height 

 of only 7400 feet to the determination of the probable tempera- 

 ture of meteorites in extra-terrestrial space. As he expresses a 

 desire to know whether any similar results have been found in 

 India, and as I have on several occasions during the past ten 

 years discussed the vertical distribution of temperature and pres- 

 sure in this country, I gladly take this opportunity of referring 

 him to my papers on the meteorology of the North-West 

 Himalaya, and on the temperature of North- Western India, 

 published in the "Indian Meteorological Memoirs," vols. i. and 

 ii. From the latter I extract the following table on the mean 

 decrement of temperature up to a height of 12,000 feet, com- 

 puted from the observations of twenty-five stations combined 

 in various ways. For each month an interpolation formula of 

 the form 



r= T'o ■^ ah + b>i- + ch^, 



was computed, and by its means the decrements from sea-level 

 to 1000 feet, 1000 to 2000 feet, &c., were calculated. Finally, 

 the aver.age decrement for the twelve months was computed, and 

 is here given in an abridged form. The curves for the several 

 rhonths dift'er very widely from one another, those for the 

 summer giving the most rapid decrement at sea-level, and the 

 decrement increasing with altitude in winter : — 



Height 

 Feet 



o to 2000 



2000 to 4000 



4000 to 6000 



6000 to 8000 



8000 to 1 0000 

 1 0000 to 12000 



616 



5S7 

 561 



5-37 



5-16 



4-9 



The mean height of the barometer at sea-level in the region 

 in question, the centre of which lies a little north of Simla, is 

 about 29"8 inches ; the mean at 6ooo feet is 24^1 inches, and 

 the mean at 12,000 feet about 19^4 inches. With these data, 

 and .adopting Mr. Hall's formula 



iT=\.iP + iJ..{5P)-, 

 we find A = 2° '979 and fj. = o°'02. These coefficients do not 

 differ widely from Sir. Hall's values, which are 2°'92 and o°'o8 

 respectively. .A.t the limit of the atmosphere, where SP = 29" '8, 

 5 7" would be - 106° '5, which would give, as the mean tempera- 

 ture ot external space, about - 30° F., the mean temperature at 

 sea-level being 77° F. 



Taking the simplest formula, 87^= \.SP, we find A. = 3°'19, 

 which is almost identical with the value quoted by Mr. Hall 

 from an early volume of Nature, but which, if it held good to 

 the limit of the atmosphere, would make the temperature of 

 external space about - 18° F., since the mean temperature at 

 sea-level is 77° F. 



The only conclusion to be drawn from such observations 

 is that the vertical decrement of temperature on mountains 

 varies greatly with locality as well as season, and the results 



