108 



KNOWLEDGE. 



[May, 1901. 



Carinae. in 1895; Nova Centam-i, in 1895; Nova 

 Sagittarii, in 1898; Nova Aquilae, in 1899; and Nova 

 Persei in 1901. The second and last of these, which 

 were much blighter than the others, were found visually 

 by Dr. Anderson. All the others were found by Mrs. 

 Fleming, from an examination of the Di-aper Memorial 

 Photographs. Edward C. Pickering. 



In Harvard Circular No. 57, Prof. Pickering gives re- 

 productions of photographs of a part of Perseus, one 

 taken before the appearance of the nova and another 

 when it far outshone all other stars in the field. The 

 great change in the spectrum which took place between 

 February 22 and 24 is also very forcibly illustrated by 

 copies of the spectra photographed on these dates. 



Numerous photographs have been obtained at the 

 Yerkes Observatoiy. but details of the measurements 

 have not yet been published. From a preliminary 

 examination. Prof. Hale appears to be inclined to at- 

 tribute the three principal green lines near F to the two 

 nebular lines and magnesium b, but Sir Norman Lockyer 

 considers that during the early stages these were 

 really due to iron vapour at a high temperature. 



The observations of magnitude which have been made 

 by various observers indicate very remarkable fluctua- 

 tions in the brightness of the new star. The rise from 

 invisibility was even more rajiid than could be assumed 

 from the evidence of the Harvard plates. It fortunately 

 happened that the region of the nova was photographed 

 by Mr. Stanley Williams only 28 hours before the 

 discovery by Dr. Andei-son, and at that time the star 

 was certainly below the 12th magnitude. The star thus 

 probably rose not less than 12i magnitudes within three 

 davs. corresponding to a multiplication of its light by 

 100,000 times. 



From the time of maximum brilliancy on Febriiary 

 23 the decline was pretty rapid until about March 13 

 when the star was not far from 4th magnitude ; then 

 until the Nth there was a slow reduction to about 4.2, 

 and the star remained near this until March 31st, 

 except that on the 19th, 22nd, 25th, and 28th it went 

 down to nearly 5.5. Thus, for a short time the star was 

 a more or less regular variable, with a well-marked period 

 of about 3 days. The expected recurrence of a minimum 

 on March 31st, however, was not observed, but the 

 oscillation has since been continued with a somewhat 

 greater period and larger range of light changes. On 

 account of these rapid changes it does not seem desirable 

 to attempt the construction of a light curve until all the 

 observations have been collected, and intending observers 

 will see the importance of noting the hour as well as the 

 day of observation. 



The continued spectroscopic observations are of the 

 utmost importance. Sir Norman Lockyer states that 

 between the 10th of March and the 25th the photo- 

 graphic spectrum had greatly changed. Besides the 

 persistent lines of hydrogen, there were lines due to 

 helium, and others possibly identical with some of tlie 

 lines in the spectra of bright line stars and nebulse, the 

 bright lines other than those of hydrogen seen in the 

 earlier photographs having disappeared. In the visual 

 spectrum it was observed that while the whole was be- 

 coming enfeebled, the bright hydrogen lines remained 

 the most prominent feature, the other lines previously 

 visible being much reduced in intensity, and appai-ently 

 also being replaced by new ones, among which was a 

 line in the orange (possibly D, replacing D). Another 

 line in the green, near \ .501. which becanu* relatively 

 brighter, was probably the chief line of the nebular 



spectrum. A preliminary reduction of a photograph of 

 the changed spectrum is thus described by Sir Norman 

 Lockyer : — 



X 387 Broad and merging into H? 3869. 



436 Faint. 



447 Not very strong. Probably helium 4471.6. 



456 Faint. 



464 Very strong broad line. Possibly the 

 465 line of the bright line stars. 



468 Moderately strong. Possibly new hydro- 

 gen, A 4686, seen in bright liue stars. 



i7l Weak. Probably helium, A 4713. 

 The lines of hydrogen shown in the photograph were 

 H/3, Hy, HS, He and H i^. These exhibited a structure quite 

 different from that shown in the earlier photographs, and 

 the place of maximum intensity had changed from the 

 more to the less refrangible side of the line in each case. 

 It thus ajopears that the spectrum has already ex- 

 hibited three distinct phases. In the first (February 

 22 and 23) dark lines on a strong continuous background 

 were the most prominent feature, and there is evidence 

 that those not due to hydrogen and helium were high 

 temperature lines of various metals. The second stage 

 (February 24 to March 10) corresponded very closely 

 with that of Nova Aurigce before its assumption of the 

 nebular condition, the spectrum consisting of bright and 

 dark lines, and many of the bright lines having dark 

 ones on their more refrangible sides. At the third stage, 

 which commenced somewhere between March 10 and 

 March 25, the spectrum consisted chiefly of bright lines, 

 some of which were probably identical with lines which 

 appear in the spectra of nebulse and bright line stars. 

 Father Sidgreaves appears to have discovered variations 

 of spectrum accompanying the changes of magnitude 

 which have occurred since the middle of March, but 

 details are not yet available. In the case of Nova Aungfe, 

 only the second of these stages appears to have been 

 recorded, the transition to the more complete nebular 

 condition indicated by the third stage of Nova Persei 

 either having been vei-y sudden or having escaped de- 

 tection from other causes. 



It will thus be seen that there is every reason to hope 

 for great additions to our knowledge, when full details 

 of the observations become available for discussion. 



A. F. 



Hctters. 



[The Editors do uot hold themselves responsible for the opinions 

 or statements of correspondents.] 



SUNSPOTS AND TERRESTRIAL TEMPERATURE. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — In comparing the temperature-tables for the 

 last 20 years, I have been struck by the fact that our 

 temperatin-e is surprisingly dependent on the number 

 of sunspots on the sun. The winters during and after 

 a sunspot minimum are notably colder than the average, 

 while the winters during and after a maximum are on 

 the whole of a mild nature. Now presuming that this 

 is not an accidental coincidence, which it seems to me 

 is most improbable, as during the last 50 years the same 

 striking connection meets us nearly everywhere, the 

 cause of this mysterious connection seems very inex- 

 plicable according to the hypothesis that solar spots 

 are excavations in the sun, produced by an eruption of 

 gases, which become highly condensed, and therefore 



