5IO 



NATURE 



[March 30, 189; 



Saturn ; as it would appear that without making some such 

 supposition, no definite limit can be fixed. 



Applying this supposition to the sun, with reference to 

 meteoric swarms, we have 2*44 times the sun's radius, taken at 

 433,000 miles, or 1,056,520 miles as the distance at which the 

 sun would prevent the meteors coalescing to form a planet. In 

 Note 3 Prof. Darwin states this at one-tenth of the earth's dis- 

 tance from the sun, probably by inadvertence. G. R. 



The Ordnance Survey and Geological Faults. 



In view of the re-survey of the United Kingdom, it seems to 

 me that if the officers of the Survey were directed to take special 

 notice of the levels of the former survey on both sides of great 

 geological faults, and to compare these levels now so as to as- 

 certain if any appreciable relative change had taken place during 

 the forty or fifty years since the first survey, valuable information 

 as to the motion of these faults, if any, might be obtained. 



This idea is mainly suggested to me by the fact that in this 

 neighbourhood a great fault intersects the Old Red Sandstone 

 close to its contact with the Highland schists, it has been traced 

 from Stonehaven on the east coast to Loch Lomond on the west, 

 and seems to give remarkable evidence of being, at least to a 

 certain extent, in motion. The village of Comrie, famous for its 

 " earthquakes," is situated on this fault, and the " earthquakes " 

 are as lively as ever. In the valley of Strathmore farmhouses 

 placed in the proximity of this great dislocation are, or were, 

 celebrated for being *' haunted," on account of the noises and 

 tremors by which the inhabitants are from time to time 

 alarmed. 



Most, if not all, British "earthquakes" have been, I think, 

 wisely attributed to similar cau-es. 



Of course fifty years is a very minute part of the history of one 

 of these old faults, but if the data of the Ordnance Survey be so 

 accurate as is usually supposed, some trace of shifting might 

 possibly be discovered if the necessary observations were made. 



Newport, Fife, March 18. Jas. Durham. 



The Discovery of the Potential. 



Mr. E. J. RouTH has lately published a most valuable 

 " Treatise on Analytical Statics." I quote from the second 

 volume, p. 17, the following note : — 



" The earliest use of the function now called the potential, is 

 due to Legendre in 1784, who refers to it when discussing the 

 attraction of a solid of revolution. Legendre, however, ex- 

 pressly ascribes the introduction of the function to Laplace, and 

 quotes from him the theorem connecting the components of 

 attraction with the differential coefficients of the function. The 

 name. Potential, was first used by Green," etc. 



From this note it appears that the discovery of the potential 

 must be attributed to Laplace. This is a wrong opinion, and 

 some fifteen years ago Baltzer proved that the introduction of 

 the function is due to Lagrange (" Zur Geschichte des Poten- 

 tials," in yournalfiir diereineund angeivandte Mathematik, vol. 

 Ixxxvi. p. 213, 1878). Some historical documents in favour of 

 Lagrange's priority have been found, by the writer of these lines, 

 in Todhunter's "History of the Mathematical Theories of 

 Attraction and the Figure of the Earth," and collected in a note 

 at the end of vol. i. of his work, " II Problema Meccanico della 

 Figura della Terra " (Torino, 1880), where a full account of the 

 early history of the potential is given, with numerous biblio- 

 graphical indications. Ottavio Zanotti Bianco. 



Private Docent in the University of Turin, 

 March 21. 



The historical note on p. 17 of my " Statics " is chiefly founded 

 on the statements in Todhunter's "History," and in Thomson and 

 Tait's "Natural Philosophy." The references to these two writers 

 are given in the note. Both Dr. Todhunter and Lord Kelvin 

 ascribe the introduction of the function for gravitation to Lap- 

 lace, and assert that the name of " Potential " was first given to 

 it by Green. My own reading, though not so extensive as 

 theirs, had not led me to form any different opinion. In Nichol's 

 " Cyclopaedia of the Physical Sciences " the first introduction is 

 given as due chiefly to Legendre, Lagrange, Laplace, and 

 Poisson. In Chambers's " Cyclopaedia" Laplace's name alone is 

 mentioned. Baltzer, as cited by Mr. Bianco, mentions the use 

 of the function by Lagrange in the Mem. de Berlin, 1777. This 

 is earlier than the memoir of Legendre, but as Legendre assigns 



NO. 1222, VOL. 47] 



the introduction of the function to Laplace, it is difficult to- 

 compare the dates. I am at present unable to refer either to 

 the memoir of Lagrange or to the treatise of Mr. Bianco. 



E. J. ROUTH. 



Van't Hoff's "Stereochemistry." 

 The review of the above by " F. R. J." in Nature, p. 

 436, raises some important points in connection with this 

 peculiarly fascinating branch of chemical science. In referring 

 to the recent ingenious and attractive theory of P. A. Guye, 

 that the numerical value of optical activity is dependent upon 

 the relative masses of the four groups attached to the asym- 

 metric carbon atom, and which carries with it the corollary that 

 if two of these four groups are of equal mass the rotatory power 

 will cease, your reviewer states that Guye " was unable to verify 

 this view in all strictness." I think, however, that he hardly 

 emphasises sufficiently that this important corollary has in every 

 case, when put to the test of direct experiment, broken down. 

 As far as I am aware, there is not a single instance of an asym- 

 metric carbon atom attached to four groups qualitatively 

 distinct, being found optically inactive in consequence of two of 

 those groups being (jtiantitatively equal in mass. Indeed some 

 such substances are not merely active but powerfully so. The 

 reviewer considers that this inadequacy of Guye's theory is 

 palliated by the alleged fact that the amount of rotatory power of 

 the esters of an active acid is determined by the weight of the 

 alkyl-group. This point, which is one of the cardinal pillars of 

 Guye's theory, I have recently put to the test of actual experi- 

 ment, by measuring the rotatory power of a number of the esters 

 of active glyceric acid, which have been prepared by Mr. J. 

 MacGregor and myself. In this investigation we found the most 

 I extraordinary verification of Guye's theory, as far as the optical 

 properties of the normal series of methyl, ethyl, and propyl 

 glycerates were concerned ; with the appearance of isomerism, 

 however, this regularity ceases, thus the isopropyl glycerate has 

 a markedly lower rotation than the normal one, whilst 

 the normal and secondary butyl compounds have a 

 lower rotation than the isobutyl ester. Nor are these differ- 

 ences consistently explicable by taking into consideration the 

 interatomic distances, as measured by atomic volume, for the 

 molecular volume of the normal propyl glycerate with its greater 

 rotation is less than that of the isopropyl compound with its 

 smaller rotation, whilst the molecular volumes of the isobutyl 

 and secondary butyl glycerates are almost exactly equal, although 

 the rotation of the former is much greater than that of the 

 latter. 



The reviewer, in referring to the rotation exhibited by the 

 salts of active acids, states that in the case of tartaric acid all the 

 salts "display in solution the same rotatory power, irrespective 

 of the atomic weight of the metal," and is apparently satisfied that 

 " the clue to this anomaly is furnished by the electrolytic theory 

 of Arrhenius," according to which " it is the ion C02(CH0H).s 

 COo which is alone responsible for the rotation." The reviewer 

 has "in this endorsed the method of special pleading adopted by 

 the advocates of this theory, in which the metallic tartrates have 

 been summoned as witnesses, whilst only the testimony of those 

 favourable to the theory has been admitted. Thus one of the 

 commonest of the metallic salts of tartaric acid — tartar emetic — 

 has a rotation which differs entirely from that of the other tar- 

 trates, and thus conclusively negatives the dogma that the rota- 

 tion of the solutions of metallic salts is independent of the 

 particular metal which has replaced the hydrogen of the acid. 

 Fresh light has been thrown on this point in the course of an 

 investigation, which I have recently carried out with Mr. Apple- 

 yard on the rotatory power of the metallic salts of active glyceric 

 acid, and which has shown that the specific rotatory power of the 

 glyceric acid has one value when deduced from the rotations of 

 its alkaline salts (lithium, ammonium, sodium, 'and potassium), 

 another value when deduced from the salts of the alkaline earths 

 (calcium, strontium, and barium), land a third from the salts 

 of the magnesium group of metals (magnesium, zinc, and cad- 

 mium). Now it so happens that almost the only salts of tartaric 

 acid which have had their rotation determined are those of the 

 alkaline metals, which also in the case of glyceric acid yield 

 practically the same rotation. Hence if only the rotations of 

 the alkaline glycerates had been determined, the same erroneous 

 conclusion would have been arrived at concerning the rotation 

 of glyceric acid. Whatever may be the^ltimate interpretation 

 put upon these new results, and I prefer for the present to ab- 



