Nov. 30, 1883.] 



♦ KNOWLEDGE * 



337 



" Let Knowledge grow from more to more." — Aifeed Tennyson. 



Only a small proportion of Letters received can possibly ie in- 

 serted. Correspondents must not be offended, therefore, should their 

 letterf. not appear. 



All Editorial communications should he addressed to the Editor op 

 Knowledge ; all Business commii/tiications to the Publishers, at the 

 Office, 74, Oreat Queen-street, W.C. If this is not attended to 



DELAYS ARISE FOR WHICH THE EDITOR IS NOT RESPONSIBLE. 



All Hemittances, Cheques, and Post Office Orders should be made 

 payable to Messrs. Wyman & Sons. 



The Editor is not responsible for the opinions of correspondents. 



No COMMUNICATIONS ARE ANSWERED BY POST, EVEN THOUGH STAMPED 

 AND DIRECTED ENVELOPE BE ENCLOSED. 



ORDNANCE MAP MEASUREMENTS. 



[1025] — I see " E. H. 0." is not a surveyor, but his letter opens 

 up an interesting question. 



It is absolutely necessary in surveying hilly land to reduce all 

 measurements to a horizontal datum. Land in such situations is 

 always bought and sold in accordance with that rule. Thus, an 

 acre of land on a hillside is really greater than an acre in the 

 level, although the additional yards it may contain may be stated 

 as the unavailable portion. 



Let us briefly consider a case. 



" E. H. O." buys a level field surrounded by a fence in the shape 

 of a perfect square whose side is 10 chains. The area of the 

 field is 10 acres. Through a convulsion of nature a large mound is 

 thrown up in the centre, two or three hundred feet in height, 

 leaving the fences undisturbed. 



The area of the surface now contained is obviously greater than 

 before, although a surveyor would take no notice of this fact, but 

 would make the area 10 acres, as originally. 



The necessity for adopting this system of surveying will be seen 

 on considering the diagram. 



JO CHfimt 



PLAN 



SECTIONS 



A H C D is a square whose side is 10 chains in length ; the mound 

 is sliown by dotted line< in the centre. On measuring the lino E ¥ 

 along the surface of i ho ground its length is found to be greater 

 than 10 chains, and this length set off from E would extend to F, 

 distorting the fence which wo know has not changed its position, 

 and bringing it nearer the point G, which wo also know ia not the 

 case. The necessity for reducing the measurements to a horizontal 

 dntuTn is at once seen. 



I have stated that tho additional area enclosed is unavailable ; if 

 we examine the sections A B, EF this is obvious. " E. U. 0." 

 cannot put iqi m..ie houses, cannot grow more trees, nay, be cannot 



get more corn off his field with the additional superficial area, than 

 he could when his field was flat. He would not care to pay for 

 having the luxury of the hypotenuse of a triangle under his drawing- 

 room floor instead of a level line, neither would he thank any one 

 for the present of a few acres on the face of a cliff. The ordnance 

 survey is quite right ; the surveyors do, as the astronomers do, take 

 the mean circumference of the earth. Astronomers do not take the 

 measurements of the circumference of the earth, up and down the 

 mountain sides. The levels and contour lines on the plans show 

 the hills. Ch.^lk. 



POSTAGE STAMP FORGERIES. 



[1026] — I am enabled to inform you that, in consequence of the 

 action of the press, combined with the refusal of the person re- 

 ferred to in the following letter to deal with forged stamps in any 

 way, and the subjoined note from myself to the Postmaster- 

 General, the postal authorities have put in motion the Act of Par- 

 liament of 1H40, whereby the possession of, or attempt to sell or 

 dispose, byany means, of any forged stamp, or representation of 

 a stamp, or the means for producing a forged stamp, is constituted 

 a felony, the penalty for which is five to twenty years' penal 

 servitude. 



Philatelists may now congratulate themselves upon being pro- 

 tected from being duped by "facsimiles" or " copies "—which 

 simply mean forgeries— of stamps of any description. They have 

 the simple, immediate remedy of communicating the brief facta of 

 their case, postage free, to "the Secretary's Office, Post-office, 

 London," in the event of any sale, or offer of sale of any kind of 

 forged stamp. Nemesis. 



[Copy of letter referred to above.] 



To the Right. Hon. H. Fawcett, M.P. Nov. 2, 1883. 



Sir, — I have the honour to enclose for your inspection a forged 

 postage stamp which has been offered for sale as being a genuine 

 "Hong Kong" 16 c. stamp. As there are thousands of persons 

 who would be glad to purchase this stamp, believing it to be a 

 genuine British Colonial stamp, especially as it purports to be 

 authenticated by the Post-Oflice obliterating si^amp, may I ask 

 if you, as the head of the postal system, are disposed to afford 

 any official aid to prevent the sale of these forgeries? and 

 thereby guard thousands of intelligent young collectors of stamps 

 from further fraud and imposition. As some evidence of the ex- 

 tent of this trade in postal and fiscal forgeries, 1 can inform you 

 that one dealer in stamps alone* has now in his possession above 

 10,000 forged stamps, chiefly British, many bearing the oflScial 

 post-mark. These forgeries have been collected at great cost, and 

 to give some idea of this cost, if these forgeries were again to be 

 sold to stamp purchasers they would readily sell for at least 

 £1,500! — a large sum for the public to be victimised out of.— 

 Respectfully waiting the honour of your early reply, &c., 



Nemesis. 



A STRANGE PHENOMENON— JUPITER'S SATELLITES. 

 [1027]— The letter (1019) of "Major ab Adversis," on p. 322, 

 suggests to me to sav that I myself received yesterday a letter 

 dated October 31, from Kamptee, in the Madras Presidency, from 

 which I extract the following :—" Extraordinary after-glow very 

 nearly every evening. After sunset and after the sky got dark, it 

 gradiially reassumes the most brilliant roseate hues, which last 

 some time. Also sun used to be green in the morning. Natives 

 say sickness, famine, end of the world, and all sorts of tilings. 

 Have you had anything like it f " Now, it is just because we have 

 had something like this abnormal after-glow— in fact, the identical 

 phenomenon— here in Sussex within the last two or three weeks 

 that I trouble vou with this communication. I first saw it after 

 sunset on the night of November 8, when it assumed the appear- 

 ance of an auroral glow over that part of the horizon below which 

 the sun must have been situated. Its brilliance was so remarkable 

 that a friend (Dr. Trentler, of Fletching), who had been with me 

 in my observatorv, and liad left, returned on purpose to ln^^te my 

 attention to what he (a skilled meteorologist) regarded as a beau- 

 tiful display of the Aurora. The whole of the western sky was 

 ablaze with the most vivid crimson glow ; albeit the sun had set 

 for more than an hour and a half. A repetition of this striking 

 phenomenon on the succeeding evening (the Sith) enabled me, how- 

 ever, to trace it detinitolv to the sun. I have not seen it since. 



It needs a certain atnount of temerity to differ with any one 

 possessing such intimate familiarity with astronomical facts as the 

 Editor of Knowledge ; but I would venture to remark, in connec- 

 tion with his footnote to Letter 1024 (p. 823), that, while fully 

 agreeing with him as to the instability of Jupiter's apparent sur- 

 face, I do not think that we need go beyond the inaccuracy of 



• We have omitted the name for sufficient reasons. 



