224 



KNOWLEDGE. 



[October 1, 1900. 



reminded by our daily experience, that what is every- 

 body's business is nobody's business. Work which 

 someone is obliged to do, or is paid to do, gets done. 

 Work too which is only open to a few to undertake 

 also generally finds that some of that few will undertake 

 it. But that which is open to everybody and yet to 

 which no one is appointed, nobody driven, hangs fii^e 

 and is left undone. 



To take one example, one of the very earliest achieve- 

 ments of astronomy was to determine the length of 

 the year. This was done long ages ago, earlier than we 

 have any record. But it was a necessary or at any rate 

 a very practical and useful work, and consequently was 

 done at an early epoch. Take again a modern instance 

 — the observation of double stai-s. This is a work which 

 is by no means within everybody's reach. A powerful 

 telescope, well mounted, clock driven, and furnished 

 with a good micrometer, is the luxury of the few. But 

 in spite of, perhaps we should rather say because of 

 this restriction, double star observation has always found 

 a number of ardent followers. So that, although it is 

 but 120 years since this branch of astronomy took its 

 rise, it has already made a most amazing progress. 



On the other hand, the various branches of naked eye 

 astronomv, branches open to every one who had eyes 

 to see and a good atmosphere, have been left almost 

 unworked. The departments of meteoric and variable 

 star astronomy are the only two in which great and 

 substantial progress has been made, and in both cases 

 such progress has been the work of the last few years. 



There need therefore be no surprise that the study 

 of auroree has not yet received the attention which 

 is its due. A certain progress has been made, and it 

 has had some very earnest and able workers, but the 

 " Astronomer without a Telescope " who should take up 

 this subject would find that he was by no means a 

 gleaner in a closely reaped field. 



The points which have been established ai'e of great 

 importance. First of all, we know that though, strictly 

 speaking, meteorological phenomena, aurorae have a close 

 astronomical connection. They vary in number as 

 obsei-\'ed in any given locality in accordance with the 

 sunspot cycle. More than that, they are evidently in 

 the closest sympathy with the distm-bances which take 

 place in terrestrial magnetism. The present time there- 

 fore is not a specially favourable one to attempt their 

 observation in these latitudes, since they are practically 

 non-occurrent in England at the sunspot minimum 

 through one of which we are now passing. Yet just as 

 magnetic storms have their greatest amplitude and occur 

 most frequently near the equinoxes so it is with aurorse, 

 and October is the most prolific month of the year. 



Auroral observation demands, beside good eyesight, 

 au observing station remote from the glare of towns 

 and artificial lights. The stories are common enough 

 of fire engines being turned out to quench an aurora, 

 and. on the other hand, it has not seldom happened that 

 a very mundane conflagration has passed muster for 

 " celestial display." " In the Memoirs of Baron Stock- 

 mai' an amusing anecdote is related cf one HeiT von 

 Radowitz, who was given to making the most of easily 

 picked up information. A friend of the Bai'on's went 

 to an evening pai-tj" near Frankfort, where he expected 

 to meet Herr von Radowitz. On his way he saw a 

 barn burning, stopped his caiTiage, assisted the people, 

 and waited till the flames were nearly extinguished. 

 When he arrived at his friend's house he found Herr 

 von Radowitz, who had previously taken the party to 



the top of the building to see an aurora, dilating on 

 teiTCstrial magnetism, electricity, and so forth. 

 Radowitz asked Stockmar's friend, ' Have you seen the 

 beautiful Aurora Borealis?' He replied, 'Certainly; 

 I was there myself; it will soon be over.' An explana- 

 tion followed as to the barn on fire. Radowitz was silent 

 some ten minutes, then he took up his hat. and quietly 

 disappeared. ' 



Granted the suitable position the most impoiiant con- 

 sideration for the student of aurorfe to bear in mind 

 is the absolute necessity for keeping as systematic a 

 watch as possible. The general agreement between the 

 cycles of sunspots, of magnetic variation and of aurorse 

 is clearly established, but there are many questions 

 ai'ising as to the connection between their minor 

 fluctuations. Now the observation of the magnetic 

 elements is perfectly continuous. Self-recording magnets 

 are set up at many observatoi-ies, and supply us year iu 

 and year out with an unbroken register. Our record 

 of the state of the sun's surface is practically continuous 

 also, but from the nature of the case aui-orse cannot be 

 presented in the same manner. The chronicle is broken 

 by the intei-^-ention of cloudy nights. It is weighted 

 by the diflference in length of darkness between winter 

 and summer. Further, it is difficult to express our 

 auroral obsei-\'ations on a perfectly uniform numerical 

 scale. One year may have a poor record, either because 

 aurorze were actually rare, or because the observer was 

 remiss or the weather unfortunate. Another year may 

 present a fallacious appearance of abundance simply 

 because the observer was more diligent or more lucky 

 in the circumstances of his observations. In a word, 

 the accidental errors of the work are large, and it there- 

 fore becomes the first duty of the student to keep his 

 own personal part in the matter as systematic and as 

 free from accident as he can. 



This is the first essential, and the observer therefore 

 should draw up a scheme for himself for the examination 

 of the sky at certain definite hours, and for certain fixed 

 intervals, to which he should adhere with the gi-eatest 

 possible regularity. There is no need for him to make 

 any great inroad into the ordinaiy hours of rest, as the 

 meteoric observer must do. or that his watches should 

 be vei-y prolonged. It will be sufficient if they are 

 perfectly regular. 



It is much to be desired that auroral obsei-vers 

 should be scattered as widely as possible, that we may 

 be able to present not merely the auroral conditions for 

 a single place, but for the entire planet. It has already 

 been discovered that they are most frequent in two 

 zones, one in the northern and one in the southern hemi- 

 sphere, and that these zones shift their position with 

 the progi-ess of the cycle. In mid-latitudes as in 

 England aurorfe are most frequent at the time of the 

 sunspot maximum. They retire polewards as the sun- 

 spot frequency declines, and are most frequent in high 

 latitudes at the sunspot minimum. The place of the 

 observer, therefore, is not a matter of indifference. A 

 broken record iu England cannot be pieced out by 

 observations in the Shetlands or in Iceland. 



But the value of a regular system of observations 

 carried on at a single station for many successive years 

 is vei-y great, and we cannot have too many observers 

 in the field. 



After the mere fact of an auroral display has been 

 noted, its duration and its average brightness ai-e points 

 to record. The duration, of coui-se, is a simple matter; 

 the brightness is more difficult, but a careful watch upon 



