December 24, 1891] 



NATURE 



189 



obtained the definition was found to be very good, but on 

 account of the difference in the lengths of the exposures given to 

 the several plates, some of them proved to be rather thin. The 

 task of developin'^ them was imposed upon Prof. Charroppin, 

 who gives a brief, interesting account of the process of their 

 development. The observations of the times of contact and the 

 study of the corona were undertaken by Prof. Engler, with the 

 aid of the French instrument. Although only two contacts were 

 recorded (the second and the fourth), he made no attempt at the 

 third, owing to the short space of time at his disposal for observ- 

 ing and sketching the corona. The drawing which he made is 

 produced (together with the other photographs) in this report, 

 and tallies, when compared with them, in nearly all respects, 

 with the exception of the two equatorial streamers on the west 

 side, that appear to extend further westward than those recorded 

 in the photographs. 



It is interesting to note in the illustrations the great similarity 

 between the corona observed in this eclipse and that of the 

 year 1878, in which year the sun-spot disturbances were at the 

 minimum. Figs, i and 2 represent the corona of the year 1889, 

 the former being a drawing by Prof. Engler, the same as the 

 one previously mentioned, while the latter is the integrated 

 result of the examination of all the photographic plates, and 

 "does not represent the corona as seen by the eye, nor as 

 shown on any one of the negatives, but is a combination of all 

 that could be found in the negatives." 



The next illustration (Fig. 3) is a sketch of the corona made 

 by Mr. Lockyer during the eclipse of 1878 (Nature, vol. 

 xviii, p. 457), and when compared with the above figures fully 

 bears out the idea that at the several periods throughout a sun- 

 spot cycle there corresponds in the corona a like period, which is 

 apparent to us only in the changes of form undergone by the 

 equatorial and polar streamers, and this only at the time of 

 eclipses. 



The following brief extracts, which we give in the observers' 

 own words, will show how the descriptions of the appearance 

 of the corona resembled one another in all the main points. 

 With regard to the structure at the north and south poles, Mr. 

 Lockyer says (Nature, vol. xviii. p. 457) : — 



" I had a magnificent view of the corona with a power 

 of 50 on my 3f-inch Cooke, and saw exquisite structure 

 at the north and south points. Curves of contrary flexure 

 started thence, and turned over, and blended with the rest of 

 the corona, which was entirely structureless and cloudlike ; the 

 filamentous tracery, which in India I observed till three minutes 

 after totality, had indeed almost gone. Prof. Bass, however, 

 tells me that by confining his attention to the same point for 

 nearly the whole time of totality, the structure came out and 

 seemed to pulsate like an aurora." 



Prof. Pritchett's account is almost the same, word for word, 

 as may be seen from the following extract :— 



" I was particularly struck," he says, "with the brilliant ap- 

 pearance in the telescope of the filaments at the north and south 

 limbs of the sun. They seemed radial at the poles, but gradually 

 bending over and merging into the equatorial streamers in passing 

 from the pole to the equator. I could not resist the impression 

 that these filaments pulsated." 



From the above it will be seen that the appearances at the 

 pole for both years were very similar ; and with regard to the 

 equatorial streamers also, their notes show that the characteristic 

 features of each coincided in almost all particulars. Owing to 

 the fact of the minimum spot period occurring at both eclipses, 

 the above results strengthen very considerably the hypothesis 

 connecting the spot cycle with the corona. 



In addition to Prof. Engler's drawing mentioned above, 

 Sefior Valle also made some eye observations of the coronal 

 streamers. The method he adopted was similar to that em- 

 ployed by Prof. Newton in 1878, and consisted in placing a 

 screen in such a position that during totality the moon and the 

 brighter corona were cut off. The photo-engraving of the 

 drawing shows an extension of the equatorial streamers to about 

 a distance of three solar diameters, while the polar regions were 

 described as of a curved luminous filamentary contraction. 



Before concluding, we must not forget to mention the admir- 

 able artotype reproductions, at the end of the report, of all 

 the negatives : as they are arranged in the order of the times of 

 exposure, they show well the progressive increase of detail on 

 the outer part of the corona as the exposure was lengthened. 



W. 



NO. II 56, VOL. 45] 



SIMPLE PROOF OF EUCLID II. 9 AND 10. 

 'Y'HE following proof of Euclid II., 9 and 10, believed to be 

 new, due to Miss Hilda Hudson, was communicated to 

 the London Mathematical Society at their last meeting. 



AB is bisected in C and divided unequally in D either in- 

 ternally (II. 9) or externally (H. 10). It is required to prove 

 that the sum of the squares on AD and DB is equal to twice the 

 sum of the squares on AC and CD. 



A C B B 



E.9. 



H 



K 



B D 



11:10. 



On AD, AC, CD, describe the squares ADEF, ACGH, 

 CDKL, all on the same side of AB. 



On FH, within the square AE, describe the square FHMN ; 

 this is equal to the square on CD. 



Let NM, KL, produced if necessary, meet in P. 



Then PE is a square equal to the square on AC. 



And»PG is a square equal to the square on DB. 



The sum of the squares on AD, DB is equal to the figures AE 

 and PG, that is to AG, PE, FM, and CK, that is to twice the 

 sum of AG, CK, that is to twice the sum of the squares on AC, 

 CO. 



SCIENTIFIC SERIALS. 

 American Meteorological JournalioT'iiiovemhtr. — Prof. H. A. 

 Hazen gives the results of three rather high balloon voyages in 

 the United States, in which he took part, (i) June 25, 1886, 

 at 7h. 50m. a.m. , a dense cloud was entered at icxx> feet, which 

 seemed like a dry fog. The temperature from the earth up to 

 more than half-way through the cloud hardly varied a degree, 

 but after that it rose rapidly. There was a region of marked 

 dampness at 7000 feet. The temperature at starting was 6i°*3, 

 and at 9640 feet it had fallen to 8° ; time, gh. i6m. (2) June li, 

 1887, at 2h. 34m. p.m., temperature 9o'''6. At 15,080 feet, it 

 had fallen to 40° ; time, 6h. i8m. p.m. Great dryness was ex- 

 perienced in the upper strata. There were two rather sharply 

 defined layers of dampness, at 7500 feet and at 12,000 feet. 

 (3) August 13, 1887, at 3h. 35m. p.m., temperature 75°-8. At 

 694ofeet itwas53°"3 ; time, 6h. 28m. p.m. The relative humidity 

 fell to 8 per cent. — Meteorology at the French Association at 

 Marseilles, by A. L. Rotch. Among the most interesting 

 papers was one by M. Crova, upon the analysis of diffused light. 

 Observations made at Montpellier at the zenith show the blue 

 to be greatest in the early morning, and least about 2 p.m., and 

 then increasing until towards evening. A cloudy sky also shows 



