May 1, 1894.] 



KNOWLEDGE 



117 



magnetic storms, as well as auroral displays, are caused by 



the passage of the earth through a dust-laden region or 



stream of matter projected from the sun beyond the 



region ordinarily occupied by the coronal streamers. — 



A. C. Eanyard.] 



— ►-♦-* — 



THE FORMATION OF DIAMONDS. 

 To the Editor of Knowledge. 



Dear Sib,— The following remarks of Dr. Joly, of 

 Dublin, who has been engaged in measuring the 

 rate at which diamonds expand on being heated, may 

 interest your readers. Commenting upon the fact that 

 the co-eflBcient of expansion increases very rapidly at 

 about 750° C, Dr. Joly remarks, in a recent communi- 

 cation to Nature, that " the sudden increase in volinue 

 at high temperatures suggests that the diamond is 

 a form of carbon which has been subjected to high 

 pressure when crystallizing. Such changes we may 

 expect to be reversible, and it is supposable that equi- 

 librium at the higher density is only preserved by 

 crystalline forces which will require to be brought into 

 play by external conditions of pressure. It is probable 

 that this is therefore an essential condition of success in 

 its artificial production. It is perhaps of interest, adds Dr. 

 Joly, that this reasoning gave rise to experiments — as I had 

 leisure for them — which I only laid aside finally upon 

 hearing of M. Moissan's success. I did not seek the aid 

 of solution in a metal, but used an apparatus to compress 

 graphite, as well as carbon prepared from sugar, between 

 iron plates kept at a red heat and urged together by the 

 alternate heating and cooling of the bars of an iron yoke. 

 I am not without hope," says Dr. Joly, " that the use of 

 high pressure at a high temperature may ultimately prove 

 sufiicient, without resort to solution in a metal, to 

 produce diamond." Yours faithfully, 



Vaughan Cornish. 



BROOKS' COMET. 

 To the Editor of Knowledge. 



Sir, — Has anyone tried to make out the correspondence 

 between the details of the two photographs of Brooks' 

 comet in the February number of Knowledge ? They are 

 so very different that it is not easy to see the connection 

 between them. It is a pity if no photographs were 

 obtained in the intervening twenty-four hours, as with 

 such a rapidly changing object as this comet was, more 

 frequent photographs are very desirable. 



I made an eye observation in the interval, but scarcely 

 any of the detail shown in the photographs was visible to 

 me. The difference between the amount that could be 

 seen and that photographed is indicated by the fact that I 

 traced the tail to a distance of just 2°, whereas in the photo- 

 graphs the total length is 3-7° on the 21st, and on the 

 22nd, including the detached portion, 4-4°. 



It may be well to give my description at that time, viz., 

 Oct. 22nd, IGh. .lOm., G.M.T. : " With power 20 on a 

 4|in. refi'actor, at first sight the tail seems strongly curved 

 (concave to preceding side), but on closer examination this 

 is found to be caused by the following part being brightest 

 to some distance from the nucleus, viz., to near the star 

 B.D. + 17°, 2496, when it fades rapidly, and a portion 

 further preceding brightens — B.D. + 17°, 2493 being at 

 the brightest part — this part seeming to be straight, and 

 continuing to be the axis to the end. The central line of 

 this part of the comet is at B.D. + 17°, 2496, or perhaps 

 slightly preceding it, and passes B.D. + 17°, 2493 and i- 

 from B.D. + 18°, 2614 to B.D. + 18°, 2617, going a little 

 beyond. The brightening of the tail about B.D. + 17°, 



2493 is an unusual feature, reminding me of the photo- 

 graphs of comet I. 1892 in Knowledge, &c. With field 

 glasses, power 4, the comet is faintly visible, and the tail 

 strongly curved, the details above described not being 

 discernible. The tail, however, is visible to the same 

 distance as with power 20." 



There can be no doubt that the bright patch I saw about 

 B.D. -f 17°, 2493, although very indefinite, must have been 

 a similar one to the two striking ones shown in the photo- 

 graph on Oct. 22nd, though it is singular I saw but one 

 instead of two. At the time of my observation, allowing 

 for the motion of the nucleus in the interval, the star 

 B.D. + 17°, 2493 would be in the axis of the south one 

 in the photograph, about ^ from its south to its north 

 extremity. Assuming that this was the 

 one I saw, and that the star was then in 

 the middle of its length (though this is 

 uncertain owing to its indefiniteaess to 

 me) the patch must have moved 17' in 

 the 8^ hours between my observation and 

 the photograph. If, however, the north 

 patch was the one I saw, a much more 

 rapid motion is in- 

 dicated ; but this 



seems improbable, + i3'2S/7,' / 



that patch not being 



in the same line • . 



from the nucleus. 



Pitting my draw- '■/ '-""^^'^ 



ing to the scale of ,,'/ 



the photograph, the 

 bright ray emana- 

 ting from the nucleus 

 and forming the 

 main part of the tail 

 for a long distance 

 fits accurately, as far 

 as it goes, on to the , 

 same in the photo- .NucUu^iij'O 



graph ; but it had ' 

 evidently o-ro'mi con- Stars traced from Barnard's photograph of 



siderflhlv in the 8-L 21st October, 1893. Axis according 



Siaei aoiy m cue O^ ^^ ^ -^ Backhouse, 22nd October, 16h. 40m. 



hours interval, lor (j.jI.T Axis of bright patch. 



it is brilliant in the 



photograph to a distance of 0-83° from the apex of the 

 head, while I could not trace it at all more than 0'53° 

 from the nucleus, thus indicating a growth of at least 

 18' in the interval. But it is singular that the preceding 

 side of the tail, joining the bright patch to the nucleus, is 

 scarcely perceptible in the photograph, while it was quite 

 plain to me. 



Allowing for the motion of the nucleus, it is remarkable 

 that the further part of the axis of the tail, as seen by me, 

 lies from 2' to 3' preceding the preceding edge of the tail in 

 the photograph on the 22nd, excepting that there appears 

 to be therein a very faint ray further preceding, in con- 

 tinuation of the preceding edge of the south bright patch. 



Yours truly, 



T. W. Backhouse. 

 West Hendon House, Sunderland. 

 April 6th, 1894. 



METHOD BY WHICH A PATIENT MAT OBSERVE A 

 CATARACT IN HIS OWN EYE. 



To the Editor of Knowledge. 

 Dear Sir, — I see from newspaper reports that the eyes 

 of Signor Crispi, Prime JVIinister of Italy, are in the same 

 condition as those of Mr. Gladstone, and that the eyes of 



