Jan. 12, 1 888] 



NA TURE 



247 



cesser, and came first to Leipzig in 181 1, the very year we are 

 concerned with ; so that in that year both men may have held 

 office, and consequently if an author's name had to be supplied 

 Baltzer might easily have made a worse guess. 



Both guess-work and circumstantial evidence, however, are 

 quite unnecessary. After these facts were received from Leipzig, 

 the library catalogue of University College, London, was turned 

 up at De Prasse's name. No " Demonstratio," it is true, rewarded 

 the searcher : but as a work with the miscellaneous-looking 

 title, "Commentationes Mathematics," 4to, Lips. 1804-12, was 

 found entered, the librarian was communicated with. In a day 

 or two an obliging reply came to hand to the effect that the lair 

 had indeed been found, the 15 quarto pages sought (or, at least, 

 as many as are essential) being pp. 89-102 in the second fasci- 

 culus. The Adl title of the whole work is "Commenta- 

 tiones Mathematicie, auctore Mauricio de Prasse, Math, 

 prof. ord. in univers. liter. Lipsiensis." The first fasciculus 

 contains 54 pages, and is dated 1804 ; the second contains 66 

 pages, viz. pp. 55-120, and is dated 1812. Of the eight 

 separate "Commentationes " the *' Demonstratio" is the seventh. 

 Doubtless, copies of this collection of mathematical papers are 

 to be found at several of the libraries above referred to. The 

 work at any rate does not appear to be rare : the writer already 

 possesses a copy, for which he paid the not extravagant sum of 

 2.r. 8(/. 



The moral on the surface of this tale may be, " Verify your 

 references " ; it is not the only moral, however. Baltzer, in his 

 first preface, felt called upon to direct attention to the many 

 inaccuracies and even errors ( " manche ungenauigkeiten und 

 selbst unrichtigkeiten " ) of Spottiswoode's pioneer treatise ; yet 

 if the leaf following the said preface be turned over, a footnote 

 of five lines is found containing five "ungenauigkeiten" (say), 

 one of which — being that referred to in the narrative of the 

 " Demon " — might well be put in a worse category. Huma^mm 

 est errare. Thomas Muir. 



Bothwell, Gla-gow, December 26, 1887. 



The Periodic Law. 



Ln none of the chemistry books or magazines to which I halve 

 nccess can I find any reference to a curious property of the 

 chemical elements in connection with the Periodic Law. If 

 instead of placing the elements as umal in seven vertical columns 

 we arrange them at distances corresponding to the differences of 

 their atomic weighty it will be found that they are disposed in 

 curious curves. The following diagram will make my meaning 



clearer. Arranging the monads in a vertical column, and taking 

 it for a base line, place Ca at a distance from K corresponding to 

 the difference of their atomic weights ; also treat Sr and Ba in 

 the same way in relation to Rb and Cs. It will then be found 



that they are arranged on a curve terminating in Li, which is 

 known to unite in itself the properties of the metals of the alkalies 

 and those of the alkaline earths. Mg, Zn, and Cd also range 

 them elves on a curve when measured from Na, Cu, and Ag. 



R.nging the tetrads vertically, we have O, S, Cr (Se?), and 

 Mo, in almost a straight line, also P, V (As?), Nb and Sb. 

 Many other curious relationships develop themselves if we plot 

 olit the elements vertically .as well as horizontally. Is there any 

 explanation of these curious curves? or is it simply accident ? 

 and if already known where can I find an account of them ? 



Do.MALu Murray. 



IleraU Office, Auckland, N.Z. 



[Would not the position of Be (Beryllium) rather affect the 

 apparent parallelism in these curves ? — Ed.] 



The Leaps of Lepus. 



While rambling in the wintertime over the snow-covered 

 plains in this region, I have recently interested myself in ascer- 

 taining how far, en a level surface, a hare or rabbit may leap at 

 each spring, at a time when either of these animals is put to 

 its best speed. Two species of Le[>us are quite abundant in 

 tliis vicinity, viz. the Mexican hare (Z. callolis callotis), and the 

 sage hare, which is really a medium-sized rabbit (Z. sylvaticus 

 Nnttalli), while the first-mentioned is a big hare. It is not cm- 

 common to find here, in certain localities, a stretch of perfectly 

 level prairie extending fcr a distance of 3 or 4 miles, and when 

 this is covered by an even layer of i inch or more of snow, it 

 offers an admirable surface on which to take account of the 

 distance which may teparate any two tracks of one of these 

 animals, either one made by a hare or one made by one of the 

 rabbits. On such a prairie as I have just referred to, I have on 

 numerous occasions fired at these animals when they have been 

 running, and at the same time beyond the range of my fowling- 

 piece ; such a shot almost invariably has the effect of so alarming 

 the game as to make it run at its very best rate of speed, 

 and. upon com'ng up with the tracks they have left on the 

 snow at such times, I have been surprised at the distances they 

 can clear at each individual leap. Under these conditions I 

 once measured the spaces cleared by an old Mexican hare, and 

 found the first two eciualled 12 feet apiece, while the third effort 

 was rather more than 13 feet, and I ha\e never known this 

 species to exceed this, although I have tested not a few of them. 

 Of course the rabbit cannot compete with such magnificent 

 gymnastics as this : it will, however, when thus frightened, 

 make leaps of fully 6 feet ; and on one occasion I measured one 

 on the dead-level prairie, which w.as rather more than 7 feet. 

 At their common rate of going, the hare rai'ely clears more than 

 4 feet at any single leap, while the rabbit is satisfied with rather 

 more than 2 feet, and, when quietly feeding about the sage- 

 brush, the tracks made by an individual of either species may 

 actually overlap each other. R. W. Shufeldt. 



Fort Wingate, New Mexic^, December 6, 1887. 



A NEW MAGNETIC SURVEY OF FRANCE} 



THE first systematic 'series of magnetic observati( ns 

 made in France was undertaken by Lamont, who 

 in 1856 and 1857 determined the absolute value of the 

 different elements at forty-four stations. The results are 

 contained in his " Uniersuchungen liber die Richtung 

 und Starke der Erdmagnetismus an Verschiedenen 

 Puncten des Siidwestlichen Europa," and are reduced to 

 three mean epochs: declination to March 1854; hori- 

 zontal component to June 1848 ; and dip to the August of 

 the same year. In 1868 and 1S69 the Rev. Father Perry 

 made a second series of observations of the intensity and 

 direction of the earth's magnetic force at thirty-three 

 stations in France (Phil. Trans., vols. clx. and clxii.). 

 Determinations of declination have also been made at 

 about twenty stations by MM. Marie-Davy and Descroix 

 in 1S75 ; and declination, dip, and intensity have been 

 observed by M. de Bernardi&res at various points along 



' 'Determination des Elements Magne'tiq-.es en France." Ouvraee accom- 

 pagr.e' de nouvelles Carles Magnetiques drestcts pour le ler Janvier. 1885 

 Par M. Th. >[oureaux, Mete'orol giste-Adjoint au Bureau Centra!, Charge 



du Service Magr.etique 

 Gauthier-Viliars, 1886.) 



a I'Observatoire du Pare Saint-Maur. (Paris ; 



