250 



KNOWLEDGE. 



[NOVEJIBER 1, 1899. 



producing a vacancy resembling the sectional contour. 

 At first sight this idea would appear to be too improbable, 

 but if we examine some of the nebulre that have been 

 photographed and presented to our view nearly as straight 

 lines because they are seen edgewise, and others seen 

 nearly edgewise and with rugged irregular surfaces which 

 are not unlike some of the outlines of these vacancies, we 

 should admit that there is some force in this suggestion. 

 This nebula presents, roughly, a circular surface with a 

 large gap cut out of it on the vorth folloiiitifi side. It 

 measures about twenty-two minutes of arc from south 

 foUmrimi to north precciUwi, and eighteen minutes from 

 vorth followijtff to ■'^outh prccedinr/. On the south, sotilh 

 foUowimi and onwards to -north folloirimi, is an extensive 

 faint cloud of nebulosity more than one and a half degrees 

 in extent, and apparently connected by faint streams of 

 nebulous matter with the nebula just described. It curves 

 round the fiducial star (..), and almost touches fiducial 



star (•.•). 



The surfaces of these nebulaj are strewn with numerous 

 stars besides the nebulous condensations which are, doubt- 

 less, involved in the nebulosity, but it is probable that the 

 stars are not involved, and are placed either behind or else 

 in front between the earth and the nebulfe. 



The stars that are shown to be distorted on the photo- 

 graph are double or multiple stars, although it does not 

 follow that they are physically connected, and it will be 

 many years hence before this can be either proved or dis- 

 proved because of their vast distances from the earth. 



THE NOVEMBER METEORS OF 1899. 



THE predicted time of maximum of the November 

 meteors is November 15th, 1899, at 18h. Green- 

 wich mean time. As a similar shower may not 

 occur again for thirty years, no pains should be 

 spared to secure the best possible observations. 

 The most useful observations that can be made by amateurs 

 are those which will serve to determine the number of 

 meteors visible per hour throughout the entire duration of 

 the shower. Circular No. 81 was accordingly distributed 

 last year, and numerous valuable observations were thus 

 secured from observers in all parts of the world. The 

 results are now being discussed by Professor W. H. 

 Pickering, and will be published later in the Annals 

 of the Harvard Observatory. Similar observations are 

 desired this year, and it is hoped that they may be made 

 on November 1.5th, and also on the two preceding and 

 following evenings. The most important time for obser- 

 vation is from midnight until dawn, as comparatively few 

 meteors are expected earlier. Observations are particularly 

 needed at hours when they cannot be made at the observa- 

 tories of Europe and America. In general, the time 

 required for ten or more meteors to appear in the region 

 covered by the accompanying map should be recorded. 

 This observation should be repeated every hour or half- 

 hour. If the meteors are too numerous to count all those 

 appearing upon the map, the observer should confine his 

 attention exclusively to some small region such as that 

 included between the stars ju, Ursae Majoris, 40 Lyncis, 

 and a Leonis. If the meteors occur but seldom, one 

 every five minutes, for instance, the time and class of each 

 meteor should be recorded. Also, note the time during 

 which the sky was watched and no meteors seen, and the 

 time during which that portion of the sky was obscured 

 by clouds. Passing clouds or haze, during the time of 

 observation should also be recorded. The date should be 

 the astronomical day, beginning at noon, that is, the date 

 of early morning observations should be that oi the 



preceding evening. Specify what time is used, as Green- 

 wich, Standard, or Local Time. When a meteor bursts, 

 make a second observation of its light and colour, and when 

 it leaves a trail, record the motion of the latter by chart- 

 ing the neighbouring stars, and sketching its position 

 among them at short intervals until it disappears, noting 

 the time of each observation. If the path of a meteor is 

 surely curved, record it carefully upon the map. 



On November 14th, 1898, thirty-four photographs were 

 obtained of eleven different meteors. Their discussion has 

 led to results of unexpected value. The greatest number 

 of meteors photographed by one instrument was five. 

 Only two meteors were photographed which passed outside 

 of the region covered by the map, although the total 

 region covered was three or four times as great. No meteors 

 fainter than the second magnitude were photographed. 



Photographs may be taken, first, by leaving the camera 



6 iBB&dw* 



at rest, when the images of the stars will trail over the 

 plate and appear as lines, or, secondly, attaching the 

 camera to an equatorial telescope moved by clockwork, 

 when a chart of the sky will be formed, in which the stars 

 will appear as points. A rapid-rectilinear lens is to be 

 preferred in the first case, a wide-angle lens in the second. 

 The full aperture should be used, and as large a plate as 

 can be covered. The most rapid plates are best for this 

 work ; they should be changed once an hour, and the 

 exact times of starting and stopping recorded. Care should 

 be taken to stiffen the camera by braces, so that the focus 

 will not be changed when the instrument is pointed to 

 different portions of the sky, especially if the lens is heavy. 

 If the first method is employed, the position of the camera 

 should be changed after each plate, so as to include as 

 much as possible of the region of the map on each photo- 

 graph. If pointed a little south-east of s Leonis, the 

 radiant will reach the centre of the field about the middle 

 of the exposure. A watch of the region should also be 

 kept, and the exact time of appearance and path of each 

 meteor as bright as the Pole Star should be recorded. The 

 plates should be numbered on the film side with a pencil, 

 and should be sent to this Observatory with accompanying 



