ii8 



NA TURE 



[December 3, 1891 



(2) When convinced of beholding so-called luminous clouds, 

 to what points shall attention be especially directed, and what 

 simple measurements of place, time, form, &c.. shall be carried 

 out in order to aid most usefully in the inquiry? 



In answering this question we will first consider those 

 methods of research in which the observer can obtain no instru- 

 mental aid, except only a watch, which should be a sufficiently 

 good timekeeper to estimate the time of observation to one 

 minute, when compared with the correct time within eight to 

 twelve hours after the observation. 



Such simple observations are the more useful, since it fre- 

 quently happens that in the well fitted up and prepared stations, 

 observation of the phenomena is prevented by bad weather, 

 or else that the phenomena stretch over too large an extent of 

 the earth's surface to be included in an organized series of 

 observations. The farther the stations are apart, the more 

 valuable are the most simple methods. For instance, in 

 order to get corresponding photographic observations from two 

 stations, 35 kilometres apart, such as Berlin and Nauen, the 

 •most rigid exactness, both as to time and place, must be 

 observed. 



If, however, observations are taken in Ea.st Prussia and in 

 the Rhine province respectively, a from twenty to thirty times 

 larger margin of difference as to time and place can be allowed 

 than in the foregoing case, without in any way lessening the 

 value of the result. 



So, if without preparation and instruments to hand an ob- 

 server believes he beholds luminous clouds, he must not imagine 

 that he can render no service to science by examining them 

 closely, for very possibly the most simple method may, taken 

 in conjunction with other similar observations, prove to be of 

 the greatest service. 



It is desirable, too, to look out for luminous clouds at all 

 seasons of the year, though, so far, they have only been seen in 

 summer. In the northern hemisphere they have only been 

 seen from the end of May to the beginning of August, with 

 greatest frequency and brightness in the month of July. 



During these weeks, usually two stars are seen simultaneously 

 with the luminous clouds, a star of the first magnitude, Capella, 

 and a star of the same constellation, of the second magnitude, /3 

 Aurigse. 



The brighter of the two stars, which is characteristic of 

 summer nights, in the northern horizon, sets towards the end of 

 June soon after eleven, and towards the middle of July before 

 ten, on account of the northerly direction of the meridian, and, 

 in North Germany, at a distance from the horizon of 10 to 12 

 diameters of the full moon. At almost as great a distance 

 from this bright star, and at a not very different distance 

 from the horizon, the second magnitude star follows towards the 

 ■west. 



By estimating the distances and directions of these two stars, 

 an excellent means is afforded of determining the outlines of a 

 group of luminous clouds. It is only necessary to determine 

 "how great the distance of a certain part of the outline of the 

 cloud group is from one or the other star, and in what direction 

 this line lies with regard to one or the other star, or how far the 

 line in question is above or below the prolongation of the con- 

 necting line of the two stars. A simple drawing of the course 

 of the outlines and their situation with regard to the two stars is 

 useful, even when it cannot be completed on the spot but must 

 be finished from memory. The time at which the drawing was 

 -made should be noted within one half-minute. 



If the group of clouds should be so far from the above-men- 

 tioned two stars as to make the determinations inexact, it is 

 advisable to determine the outlines of the clouds for a certain 

 time in the following way. Take up a position from which the 

 outlines of houses, trees, &c., can be seen close to the position 

 of the clouds, and fix thus the relative position of these earthly 

 objects to the position of the clouds by a simple drawing, 

 describing the spot from which the observation is made in such 

 a manner that the place occupied by the head of the observer 

 can be found again. The lines drawn from the position of the 

 observer to the outlines of the earthly objects, and the resulting 

 localization of the outline of the clouds in the heavens can then 

 be determined at once by means of simple instruments for 

 measuring angles, or on succeeding nights by the aid of a good 

 star chart. 



It is necessary to verify the exact point of time of these ob- 

 servations by comparison of the watch used with the time at a 

 telegraph office, and correction of any errors should be made to 

 the fraction of a minute. 



NO. 



I 153, VOL. 45] 



In communicating these observations, the exact place at which 

 they have been made must be accurately described. 



Should a complete observation be impossible, owing to the 

 time during which the luminous clouds are visible being too 

 short for careful measurements and drawings or to any other 

 cause, the observer should nevertheless communicate briefly to 

 the Society of Friends of Astronomy and Cosmic Physics that 

 he has seen what he believes from the foregoing considerations 

 to be luminous clouds from a certain place, in a certain direction 

 in the heavens, and within a certain quarter-hour. 



The peculiar movements hitherto observed of the clouds in 



question lead to the suggestion that perhaps a period consisting 



of several days exists, within which one and the same group of 



clouds is visible at the same hour from the same place, other 



conditions of the heavens being favourable. Every communica- 



j lion as to these phenomena will be valuable in the decision of 



j this important point, which it has hitherto been impossible to 



j settle, owing to the uncertainty of the weather and the fewness 



I of the observers. 



j Those co-operating in our branch of research who are in 

 j possession of astronomical, photographic, or other physical 

 apparatus, will of course be able to give more exact details as to 

 j place, movement, and constitution of the luminous clouds. 



Suggestions for these observations cannot be given so briefly 

 and simply ; but for the sake of full and complete agreement 

 between different observers, especially as to the point of time 

 selected for taking photographs and measurements, members of 

 the Society of Friends of Astronomy and Cosmic Physics are 

 invited to communicate with O. Jesse, Steglitz bei Berlin, 

 Albrechtsstrasse 30. This course would also be advisable in 

 the close optical examination of the clouds with regard to the 

 peculiar changes in strength of light and the degree and kind of 

 self- luminosity which they perhaps send out together with the 

 reflected sunlight. 



In the night from June 25-26 of this year the summer re- 

 appearance of the luminous clouds was observed very brightly 

 from Berlin and the neighbourhood. 



More detailed particulars on the whole subject of inquiry are 

 contained in a small paper by W. Foerster, which has been sent 

 to all the members of the Society of Friends of Astronomy and 

 Cosmic Physics. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Oxford. — Mr. G. C. Inge, Magdalen College, has been ap- 

 pointed to the Studentship offered to the University by the 

 Managing Committee of the British School of Athens, from the 

 Newton Testimonial Fund. 



The death is announced of Dn Evan Evans, Master of Pem- 

 broke College, who filled the office of Vice-Chancellor of the 

 University from 1878-82. 



Convocation has granted £2'-, towards the cost of the anti- 

 quarian researches at Chester, which are throwing great light 

 upon the obscure period of the military occupation of Britain in 

 the time of Agricola. Prof. Mommsen has appreciated the 

 value of these researches. 



At a meeting of the Junior Scientific Club, Mr. A. Colefax, 

 Christ Church, read a paper on the investigation of the change 

 taking place in acidified solutions of sodium thiosulphate. The 

 subject of hypnotism was treated by Mr. E. L. Collis, of Keble ; 

 and P. C. Mitchell had an exhibit, and offered some remarks 

 concerning primitive man in the Torquay caves. 



The University has published the official Calendar for 1892. 

 The arrangement and information contained differ little from 

 former years. We learn that the number of undergraduate 

 members of the University has increased from 31 10 to 3212. 

 The number of matriculations in 1890 were 77 r, as compared 

 with 787 in the preceding year. The number of B.A. and 

 M.A. degrees is very nearly the same as in 1889. 



SCIENTIFIC SERIALS. 

 American Journal of Science, November 1891. — The solu- 

 tion of vulcanized india-rubber, by Carl Barus. Experiments 

 have been made by the author on the solubility of india-rubber 

 in different solvents at different temperatures. Elastic sheet 

 india-rubber, such as is used for rubber bands and tubing, is not 

 fully soluble in CS, at 100° or 160°, but is quite soluble at 185°, 

 and extremely soluble at 210". It is also easily dissolved by 

 liquids of the paraffin series at 200°. Various other substances 



