>6o 



NA TURE 



{Jan. 15, 1885 



huted did the cold points on one side resemble those on the 

 other. Prof. Eillenburg farther confirmed Dr. Goldscheider's 

 conclusions that in particular parts of the skin, between the cold 

 and warm points, lay the points of pressure which were sensitive 

 10 touch but not to differences of temperature. The existence, 

 on the other hand, of special points for perceiving pain due to 

 temperature the speaker had been unable to verify. Under 

 the stimuli inadequate to temperature feeling, as the elec- 

 trical and mechanical, he had tried the electric current with 

 positive results. A moderate stream, producing in the skin the 

 well-known prickly feeling, having by means of a pointed elec- 

 trode been introduced into a cold point, generated a decided 

 feeling of cold. Mechanical stimuli, which should produce the 

 same effect, failed, however, in Prof. Eulenburg's experiments 

 to do so. 



Physical Society, December 19, 1884. — Prof. Lampe gave 

 some interesting historical notes on the calculations respecting 

 solids of attraction, the results of which he had communicated at 

 the sitting of November 21. In these problems he had started with 

 a solid of greatest attraction, in regard to which Gauss had laid 

 down the law that its attraction was related to that exercised 

 by the same mass in globular form on a point of its surface, as 

 3 : ^/ 25. This law was found briefly adduced in a note in 

 Gauss's treatise on capillarity, without any proof either there or 

 anywhere else. Although Prof. I-chellbach, who in 1S45 calcu- 

 lated the form of the body of greatest attraction, ascribed the 

 adduced law to Gauss, yet Prof. Lampe, in consideration that 

 Gauss did not prove the law referred to and introduced it with 

 the word "constat," was of opinion that it must have been 

 already proved before the time when it was cited by Gauss. He 

 had now, then, in point of fact, succeeded in tracing the author 

 of the law. It originated, namely, with John Playfair, who, in 

 1809, in a treatise "On the Solid of Greatest Attraction," had 

 calculated the form of such a body, and with reference to the 

 magnitude of its attraction had arrived at the result already 

 stated. In the same treatise John Playfair had dealt with a part 

 of the problems brought before the Society by Prof. Lampe, and 

 in respect of the cone and cylinder had come to the same results 

 as himself. In calculating, however, the attraction of an ellip- 

 soid flattened at the poles, he had, as was shown more at large 

 by the speaker, committed an error, in consequence of which he 

 had arrived at the conclusion that in the case of any eccentricity 

 of the meridians the attraction was less than in the case of 

 eccentricity o, that is, than in the case of a globe. The fact, 

 on the other hand, was that with oblateness the attraction at 

 first increased and approached to that of the solid of greatest 

 attraction, though yet without ever quite reaching it. It then 

 diminished, till finally it sank to o, when the pole coincided 

 with the middle point. Let the attraction of a homogeneous 

 mass in globular form be equal to 1, then the greatest attraction 

 which this mass was in any case able to exercise was equal to 

 I "025986, while the maximum of attraction in an oblate rotatory 

 ellipsoid was equal to 1 '02213. Whether John Playfair's error 

 had been already elsewhere observed or corrected was not known 

 to the speaker. Altogether John Playfair's treatise appeared to 

 have lapsed into oblivion, seeing that in the manuals of mechanics 

 the law o£ maximum attraction being to the attraction of a ball 

 as 3 : y/25 was universally imputed to Gauss, and the calcula- 

 tions of the solid of greatest attraction, which John Playfair had 

 already worked out, to Schellbach. — Following up this address 

 Dr. Kcenig communicated the plan of an investigation which he 

 contemplated carrying out in conjunction with Dr. Richarz. 

 The investigation had for its object to determine with greater pre- 

 cision than had hitherto been done the mean density of the earth. 

 The most exact measurements hitherto taken on this question 

 came, as was known, from Ilerr von Jolly, in Munich, who, in a 

 high tower, experimented on a balance, on one scale of which 

 hung a wire, 21m. long, bearing another scale at the bottom. 

 After balancing a body in the upper scale and then transferring 

 it to the scale 21m. lower, the body was found to be somewhat 

 heavier in the latter case in consequence of the more powerful 

 attraction there exercised on it by the earth. On next placing 

 under the lower scale a lead ball weighing no centner, and 

 repeating the experiment, he found a greater increase on the 

 upper scale weight than in the first instance. From the rela- 

 tion of these augmentations of weight and the volume and 

 specific weight of the lead ball, Herr von Jolly calculated the 

 mean density of the earth. Such a mode of measurement, 

 however, laboured under this unavoidable source of error, that 



there was no means of safe-guarding the long wire from differ- 

 ences of temperature. Dr. Kcenig and Dr. Richarz had now, 

 independently of each other, devised another method of utilising 

 the balance for the purpose of determining the mean density 

 of the earth. Instead of placing the lead ball 21 m. under the 

 upper scale, they brought the heavy body directly under the 

 upper scale, whence a line, passing through a perforation of the 

 heavy mass, bore the lower scale immediately underneath it. 

 When, now, a body was weighed in ihe upper scale, the mass of 

 lead acted in a sense similar to that of the force of gravity, and 

 its attraction was added to gravitation. When, on the other 

 other hand, a body was weighed in the lower scale, the mass of 

 lead operated in an opposite direction, and its attraction was 

 subtracted from gravitation. By this experiment, therefore, a 

 double effect was obtained from the mass of lead instead of the 

 single effect in Herr von Jolly's experiment. Again, by 

 bringing a second equally large mass of lead under the scale 

 of the other side, disposing it in the same manner as the first 

 mass, the effect of the mass of lead might be multiplied four- 

 fold. An equilibration might be made by placing the weight 

 on one side in the upper, on the other side in the lower, 

 scale. Then the weights might be transposed. Indepen- 

 dently of the advantage of a fourfold comparative estimate 

 of the attraction of the mass of lead, all disturbances due 

 to differences of temperature were by this method entirely 

 obviated. The precision of the measurement would be still 

 further enhanced by using a mass of lead of 2000 centner. 

 The total mass of lead would compose a block, the most suit- 

 able form for which had yet to be theoretically determined. In 

 the centre, above this block, would stand the balance, and the 

 wires of both scales would pass through two equal perforations, 

 at the ends of which, under the block, would depend the two 

 lower scales. The construction of such a block of lead would 

 be rendered possible by making it consist of 1300 separate 

 pieces capable of being joined together into the form desired, 

 and after a series of experiments they might be fitted up anew, 

 so as to secure compensation for any errors due to unequal in- 

 terior structure of the blocks. Of these masses of lead a parel- 

 lelopiped would have a side of 25 m. and a height of ['Sm. 

 As was self-evident, the precision of the balance was a matter 

 of extreme moment for these measurements. The mechani-t 

 who had undertaken their construction had engaged to produce 

 a sensitiveness of one hundred millionth for the weight of 1 kg. 

 used in such measurements. He had further engaged, by an 

 adequate modification of the construction, to obviate the error 

 arising from the circumstance that the edges never corresponded 

 mathematically with that term, but had always more or less 

 diameter, so that with the inclination of the beams the plane of 

 support changed. Dr. Kcenig hoped to be able in the course 

 of a year to announce the numerical results of the experiment. 



CONTENTS page 



The Earthquakes in Spain 237 



The Stability of Ships. (Illustrated) 238 



Our Book Shelf:— 



Nicols's " Natural History Sketches among the 



Carnivora, Wild and Domesticated " 240 



Kegel's " Entwickelung der Ortschaften im Thiiringer- 



wald" 241 



Letters to the Editor : — 



River Thames — Abnormal High Tides. — J. B. Red- 

 man 241 



Our Future Clocks and Watches. — Chatel. (Illus- 

 trated) 241 



The Coal Question. By Sydney Lupton 242 



Invigoration of Potatoes by Cross-Breeding . . . 246 

 On the Evolution of the Blood-Vessels of the Test 

 in the Tunicata. By W. A. Herdman. {Illus- 

 trated) 247 



Notes 249 



Our Astronomical Column : — 



The Naval Observatory, Washington 251 



The Dearborn Observatory, Chicago 251 



Geographical Notes 251 



Characteristics of the North American Flora, II. By 



Prof. Asa Gray 253 



Bryn Mawr College 255 



Scientific Serials 256 



Societies and Academies 258 



