94 



KNOWLEDGE 



[May 1, 1891. 



identical. Yet this picture (which you would not recog- 

 nize on comparison) was made from the same plate as 

 that published in the July 1890 issue of Knowledge. 



Mr. Ranyard says, at the bottom of page .^)0 (Know- 

 ledge ior JIarch 1891) : " In Mr. Barnard's picture there 

 are two clusters of stars near to the edge of the field at 

 the bottom of the plate. Only one of these clusters, v-iz. 

 that to the right hand, or western side, is shown in Mr. 

 Kussell's plates." It is the left-hand, or folloirhuj, cluster 



which is shown on Mr. Russell's picture. The right-hand 

 one is too far to the right to be shown on his plate, 

 though a small bunching of stars immediately following 

 it is visible close to the right-hand edge of the picture, 

 2-6 inches from the bottom. 



I would remark here, as a caution, that it is extremely 

 unsafe to judge of the actual relative brightness of 

 different surfaces, such as the Milky Way presents, fi'om 

 photographs which have been treated differently in point 

 of time and development. A partially brought out con- 

 figuration will have in many cases, a decidedly different 

 aspect from that of a carefully and thoroughly developed 

 one. Yom's respectfully, 



E. E. Babnabd. 



Mount Hamilton, March 16, 1891. 



[As mentioned in the March number of Knowledge, it 

 is quite easy to account, by assumed differences in the 

 method of development or differences in the sensitiveness 

 of the plates used, for the fact that so little nebulous 

 brightness is shown on Mr. Russell's plates as compared 

 with Mr. Barnard's ; but the remarkable fact which cannot 

 be so accounted for is that the relative brightness of the 

 nebulous areas on the two sets of photographs does not 

 correspond. For example : the two brightest areas on 

 Mr. Barnard's photographs are (1) towards the lower part 

 of the great tree-like structure on the preceding side, and 

 (2) a large area on the south 'following side of the tree- 

 like structure. But Mr. Russell's photographs do not 



exhibit any trace of nebulosity in these regions, while 

 there is distinct nebulosity shown in the fainter head of 

 the tree-like structure. Mr. Barnard's densely-printed 

 photograph of his own negative — which I have had repro- 

 duced as a printing-block by a photographic method — is 

 very interesting ; but I do not concur with him that t]m 

 large stars near the middle of Mr. Russell's picture " are 

 undoubtedly defects " in Mr. Russell's plate. They may 

 be due to defects in the collotype copies which I forwarded 

 to Mr. Barnard. — A. C. Raxyabd.] 



PERPETUAL CALENDARS. 

 To the Editor of Knowledge. 

 Deab Sib, — As the subject of finding the day of the week 

 for any given date appears to interest a large section of 

 the readers of your valuable magazine, I enclose for your 

 acceptance (agreeably to the promise given in your Feb- 

 ruary issue) a few rules bearing upon the subject of " Old 

 Style " dates, all of which have been verified from that 

 valuable work, Sir Harris Nicolas's Chroiwhiiiij of Histonj. 

 The rules appear to me to be as simple and correct as 

 those previously given, and moreover possess the additional 

 advantage of being serviceable " anywhere and every- 

 where " without the extraneous aid of discs or any other 

 office aid. 



Yours faithfully, 



RoBT. W. D. Cbistie. 



Fade /.—The last day of .July of any " Old Style " date 

 may be got thus : — 



Take the year, add a quarter, divide by 7. 

 K.vaiiiph' 1. — The Armenian Era commenced July iJth, 

 A.D. 5.52. On what day of the week was it ? 

 We have 552 

 add 138 



7)690 



98-1-4 = Wednesday — 31st July. 

 Thus Tuesday was the 9th July 552. 

 7i«/t! II. — Take the year, add a quarter, take away the 

 the No. of the month, di\-ide by 7. The remainder indi- 

 cates the last day of month. 



Example 1. — On what day of the week was March 31st, 

 1000? 



We have 1000 



add i 250 



1250 

 subtract 8 = No. of month of March. 



7)1217 



178 + 1 = Sunday. 

 Thus March 31st, 1000 (Easter Day), fell on Sunday. 

 E.rample 2. — King Richard I. died on Tuesday, the 6th 

 April 1199. Prove this. 

 1199 

 299 



1498 

 3 



7) 1495 



213 -t- 4 = Wednesday - 31st March. 

 Thus 6th April was on Tuesday. 



