428 



NA TURE 



[March 30, 1876 



How Typhoid Fever is Spread 



The case recently reported (Nature, vol. xiii. p. 331) by 

 Prof. Frankland from a Swiss village, where the poison of typhoid 

 fever is said " to have filtered through a mile of porous soil, but 

 which had nevertheless lost none of its virulent properties," is 

 certainly so striking that some further reference to authorities 

 seems requisite. If it can be satisfactorily proved that this was 

 the most likely and reasonable origin of the case, it will give 

 additional weight to every endeavour for preserving our water 

 supply from every conceivable impurity ; but unless based on the 

 opinion of a competent and skilled investigator of such cases, it 

 will lay us open to the charge of receiving any similar statement 

 that favours our view, however rash. As medical officers of 

 health it is our duty frequently to trace the origin of cases of this 

 disease, and my anxiety to have further information of this case 

 will thus seem reasonable, and I hope will meet with some reply 

 from the distinguished professor, J. MITCHELL WiLSON 



Rochdale, March 



The Ash Seed Screw 



Mr. Alfred George Renshaw would like to know (Nature, 

 vol. xiii. p. 367) whether the pitch of the ash seed screw is that 

 which would give most power to the propeller of a steamer. 



There is no screw on the samara of the ash {Fraxinus excel- 

 sior) while it is green. The pitch of the screw, at the same date, 

 differs on different trees, and also on different seeds of the same 

 tree, and also on different parts of the same seed. 



Why the wing generally becomes twisted as it dries is a very 

 interesting question. But what seems to me the most remark- 

 able fact about this phenomenon is, that in every case, and on 

 all trees alike, the thread of the screw is in one direction ; that 

 direction being the same as in a cork-screw, or ordinary screw- 

 nail. 



All varieties of the wild oat [Avena/atua) and the fly oat {Av. 

 sterilis) have long awns, which also in the green stage are straight, 

 but which in ripening become twisted. And in these also, the 

 direction of the screw is uniform and the same as in the ash 

 seed ; but the pitch of the screw is variable. 



Are these facts the same in other parts of the country ? Are 

 the screws left-handed on the south of the equator ? 



Summerhill, Aberdeen, March 20 A. Stephen Wilson 



OUR ASTRONOMICAL COLUMN 



The Companion of Sirius. — Mr. Wentworth Erck, 

 of Sherrington, Co. Wicklow, in a communication dated 

 March 21, notes the fact of a considerable diminution in 

 the angle of position of the small star accompanying 

 Sirius, which was detected by Alvan Clark in January, 

 1862 — since the earlier measures, and adds that he cannot 

 now estimate it at more than 55°. This retrograde motion 

 is a consequence of the theory of Dr. Auwers, supposing 

 the co7ncs to be the cause of the anomalous proper motion 

 of Sirius, which has formed the subject of several elabo- 

 rate memoirs by this eminent astronomer. His last ele- 

 ments of the presumed disturbing body, adapted to the 

 form of double star orbits, are as follow : — 



T 1843-275 



Node ... 6i°57'-8 



A i8°54';5 



Inclination 47° 8' "7 



Excentricity o*6i48 



Semi-axis 2" "331 



Period 49*399 yrs. 



Motion, retrograde. 



The following angles of position and distances are given 

 by these elements : — 



1862 'o Pos. 85-4 Dist. lo-io 



1865-0 „ 79-9 „ 10-78 



18680 „ 75-0 „ 11-15 



1871-0 „ 70-3 „ 11-20 



1874-0 Pos. 65-5 Dist. 10-95 

 18760 ,, 62-1 ,, 10-59 

 1878-0 „ 58-4 ,, 10-05 

 i88o-o „ 54-2 „ 9-33 



Dr. Auwers gives a comparison of his calculated angles 

 and distances of the centre of gravity, with those of Clark's 

 companion to 1867, the agreement being pretty close 

 throughout. But there can be no doubt that the cal- 

 culation has given the angle too great since that year. 



The Washington observations show the following differ- 

 ences : — 



In the above orbit the limits of distance are 2"*3i at 

 i84r84 for a position of 302°-5, and ii""23 at 1870-13 for 

 position 7i°"7, and Auwers remarks that under the former 

 condition the angle changes one degree in ten days, while 

 under the latter condition 233 days are required for the 

 same diminution. 



Our correspondent mentions that Lassell's "new star" 

 (Mem. R. Astron. Soc, vol. 36, p. 18), "though exceed- 

 ingly faint, was distinctly visible. Pos. circa 130°, dis- 

 tance circa 75"," with 7J inches aperture power, 200. 

 Lassell, 1865, January 14, found the position i27°-o, dis- 

 tance about one minute. 



Dr. Gylden, from the meridian-altitudes of Sirius, ob- 

 served by Sir Thomas Maclear at the Cape of Good Hope 

 during the years 1836 and 1837 found for the annual paral- 

 lax of the star o"*i93 {Bulletin deVAcad. de St. Petersbourg, 

 t. vii.). Adopting this value, Dr. Auwers finds for the 

 mean distance between the companion and Sirius, 37 

 times the earth's mean distance from the sun, and for the 

 masses of Sirius and companion 1376 and 671 respec- 

 tively, in units of the sun's mass. The parallax o"'i93 

 corresponds to 1,068, 700 times the sun's distance from the 

 earth. 



D'Arrest's Comet. — M.'L^v&rnQx's Bulletin Inter- 

 natiotial of March 18, contains the definitive elements 

 obtained by M. Leveau for the next return of this comet 

 to perihelion in 1877, with an ephemeris for every 20th 

 day throughout the year, which sufficiently defines the 

 circumstances of the next appearance. The whole of his 

 long-continued investigations relating to the motion of 

 this comet have been conducted by M. Leveau with 

 extreme care and minuteness, so that by his investiga- 

 tions, in continuation of those commenced by M. Villar- 

 ceau, the theory of D'Arrest's comet has been placed upon 

 a similar footing of accuracy to that, upon which the 

 theory of the periodical comet of Faye now stands through 

 the labours of Dr. Axell M oiler of Lund. 



The next perihelion passage of D'Arrest's comet is 

 found to occur 1877, May 10*339 M.T. at Paris, and the 

 comet appears to attain its maximum intensity of light 

 about a fortnight subsequently. Other elements of the 

 orbit which apply to 1877, Jan. 14, are : — 



O / II 



Longitude of the perihelion 319 9i5}jur 



„ „ Ascending Node ... 146 9 28 > jggQ.^" 



,, ,, laclination 15 43 9) 



,, ,, Excentricity 0-6278048 



Logarithm of perihelion distance ... o- 1 199444 

 Motion direct. 



The elements usually found in catalogues of cometary 

 orbits are here substituted for others given by M. Leveau. 



The semi-major-axis of the orbit is 3*54139, to which 

 corresponds a sidereal revolution of 2434-2 days. 



When this comet was last observed by Herr Juhus 

 Schmidt at Athens, on December 20, 1870, the intensity 

 of light was 0-154 ; the greatest intensity attained in 

 1877, about May 26, is only 0*22, and it is certain that 

 large telescopes will be required for the proper observa- 

 tion of the comet. When theoretically brightest, it rises 

 at Greenwich less than two hours before the sun, and as 

 this difference increases towards the end of the summer, 

 the intensity of light is diminished by one-half. The 

 comet will be nearest to the earth in the middle of Octo- 

 ber (distance = i'4o). M. Leveau promises in a subse- 

 quent communication a precise ephemeris for the whole 

 year, and, it may be remarked, it very rarely happens 

 that there is any necessity for predictions extending over 

 so long a period. 



