)7A 



NA TURE 



[August i 7, 1893 



screw F (Fig. 3) so as to shorten the path a e that 

 the bands at the side move in toward the centre, the 

 opposite being the case on lengthening the path A E. 

 Therefore heating the air {i.e. rendering it less dense) 

 has the same effect as shortening the path (z'.^. it accel- 

 erates the motion of the light passing along it), whilst 



Fig. 5. — Photograph of interf<^rence bands si win- i:rle t of introdiicirg 

 glowing end of match. 



cooling the air (rendering it denser) has the opposite 

 eiTect ; which demonstrates very simply the truth of 

 the undulatory as opposed to the emission theory of 

 light ; for on the latter theory the exact reverse would be 

 the case. Edwin Edser. 



THE AUGUST METEORS, 1893. 



THE Perseid shower, though it cannot rival periodical 

 displays such as the November Leonids and An- 

 dromedes when at their best, is certainly of equal interest, 

 for it forms a tolerably rich display every year, and con- 

 tinues active during several weeks from a radiant which 

 has a comet-like motion of about 1° R.A. per day east- 

 wards. A vast number of observations have been made 

 during the last half-century, but it must be confessed that 

 we have by no means completed our investigation of this 

 remarkable stream. Nor have we gained a thorough 

 knowledge of the numerous and fairly prominent minor 

 showers which contribute to render this epoch the most 

 significant and the most interesting period of the year to 

 the meteoric observer. 



Either moonlight, or cloudy wet weather, prevented my 

 obtaining any observations at the latter part of July this 

 year, and it was not until August 4 that I commenced 

 work. Moonlight was, however, pretty strong, and in a 

 watch of about half an hour I only saw four meteors, in- 

 cluding one typical Perseid from a radiant at about 

 36= + 56-. 



On the following night, August 5, the sky was much 

 clouded, but between loh. 15m. and iih. 45m. I saw, in 

 clear spaces, twelve meteors, of which four were Ferseids, 

 indicating a radiant at 39'' -(- 55". The brightest meteor 

 seen was at iih. 3m., but it appeared behind thin cloud 

 in the northern sky. It was fully equal to a ist mag. 

 star, and left a bright streak along its path from I7i° -^ 

 76' to 219^ -I- 78'. This was not a Perseid, the direction 

 of flight being from near 7 Andromeda?. 



The nights of August 6 and 7 were cloudy and no 

 observations could be secured. 



On August 8 the sky cleared and I counted 36 meteors 

 in the two hours from loh. 50m. to I2h. 50m. There were 12 

 Perseids amongst them and the radiant was well defined 

 at4i°+ 56'. At lih. 25m. a fine Perseid about equal to 

 Jupiter flashed out in the region of Polaris and left a 

 streak of nearly 20 degrees along its course. 



August 9 proved fine, but lightning was extremely fre- 

 quent and vivid during the whole night, and considerably 

 interfered with the observations It proceeded from 

 clouds low in the east and north quarters, but apart from 

 that the firmament was very clear. The day had been 

 one of excessive heat, the maximum shade temperature 

 being 84° ; the lightning which followed it may be said 

 to have been in constant play during the night, one flash 

 succeeding another with little intermission. The effect as 

 it burst through the broken clouds and lit up their 

 borders was very beautiful and so striking as to distract 

 attention from the far less imposing features of the 

 meteor shower then in progress. In the 2J hours' interval 

 between iih. 30m. and i4h. I managed, however, to 

 observe 45 meteors, including 20 Perseids from a radiant 

 which I determined as follows : — 



h. m. h. m. o 



11 30 to 12 o ... 42 -^ 56 ... 4 meteon:. 



12 o to 13 o ... 43 -I- 57 ... 9 ,, 



13 o to 14 o ... 43 -f 57 ... 7 ,, 



Adopting the mean centre as at 43° + 57°, I think the 

 position may be considered a very accurate one for the 

 date. I saw no exceptionally brilliant meteors during 

 the night, though several of the ist mng. were recorded, 

 and the Perseids struck me as being fainter than usual. 

 Most of them traversed swift short paths not very far 

 from the radiant, so that the position of it could be 

 determined very satisfactorily Mr. Booth of Leeds 

 informs me that he found the Perseid radiant at 43" + 57° 

 from 15 meteors of this shower observed on August 9. 

 This position is identical with that found at Bristol on 

 the same night. 



On August 10 the sky proved variable, but it was 

 pretty clear at times before midnight and overcast after- 

 wards. Between iih. and I2h. I noticed 21 meteor:;, of 

 which 14, or two-thirds of the whole, were Perseids, but 

 clouds interrupted work during a part of the time. After 

 I2h. it was not found possible to continue the work with 

 any further prospect of success, as clouds had obliterated 

 all but a few ist mag. stars. The Perseid radiant was 

 now found at 45' + 57", which agrees with the usual posi- 

 tion on the date of maximum. As to the character of the 

 radiation on this and previous nights,it was fairly definite 

 and exact, and limited to an area of 2° or 3°. In point 

 of activity I regarded the shower as disappointing on 

 the 5th, 8th, and 9th, but from what I saw on the loth, 

 and considering the unfavourable circumstances prevail- 

 ing at the time, the display was a tolerably conspicuous 

 one. I recorded several bright meteors on the loth, 

 and, as they may possibly have been seen elsewhere, the 

 times of apparition and observed paths are given 

 below : — 



Mag. From To Radiant. Notes. 



h. m. 



11 o 



11 21 



II 24 



II 43 



II 56 



I ... i-fii ... 264-19 ... 304 — 14 ... Slow. 



I ... 33i-f383 ... 317 + 23^ ... Perseid ... Swiff, streak. 



I ... 325 + 29 ... 314-1-15 ... Perseid ... Swift, streak. 



9 ... 42 + 5^ ... 40-1-53^ ... Pcr-^eid ... Slow, b. stre.lk. 



\ ... i40-i-84.\ ... 2JO + 70 ... Perseid ... Swift, streak. 



NO. 1242, VOL. 48] 



On August 1 1 the sky was overcast. 



On August 12 it was partly fine before I3h., but by no 

 means favourable for this class of work. I counted 24 

 meteors, including 7 Perseids with radiant at 48'-|-57^. 



On August 13 the conditions had greatly improved, and 

 after midnight there was not a cloud in the sky. Watch- 

 ing for 3J hours I recorded 43 meteors and found the 

 Perseid shower still visible from a radiant at 48-4-57'' (8 

 meteors). No exceptionally bright meteors were seen, 

 but at I3h. 5m. one about equal to Jupiter fell from 



