286 



NATURE 



\Feb. II, 1875 



Tiie Micrographic Dictionary — Pollen Grains 

 I READ your criticism of this book in last number of Nature 

 with a good deal of interest, and I fully agree with your reviewer 

 in his statement that "workers in different fields will place a 

 different estimate on the importance of their own depart- 

 ment." Allow me to call your attention to the two singularly 

 erroneous figures of the pollen grains of Miinnhis moscJialns 

 (PI. 32, Fig. 24) in this work. I have frequently examined the 

 pollen of this plant, and have never seen it anything like the 

 figures in the ''Dictionary," or in any way differing from the 

 grains of many other members of the Scrophulariacece. The 

 pollen of 71/. vwschalits is like a grain of wheat, and not like tlie 

 wonderful convolute ball shown in the "Dictionary." 



In his " Common Objects for the Microscope," Plate 3, Fig. 21, 

 the Rev. J. G. Wood reproduces the fust of these two extra- 

 ordinary figures, and describes the pollen as "belted with wide 

 and deep bands," &c., but by an oversight he omits to give 

 the source from which the erroneous figure is copied. 



In his "One Thousand Objects for the Microscope," Plate 2, 

 Fig. 6, Mr. Cooke copies the second extraordinary figure of this 

 pollen, and says, "these curious granules resemble a band or 

 cord rolled or iolded in a spherical mass," as if he had 30 seen 

 them. I'he "Dictionary" plate certainly does 1: ok like this, 

 tut in the letter-press the folds are referred to as " slits or 

 furrows." By an oversight Mr. Cooke also omits to give the 

 source from which his erroneous figure is copied. 



W. G. Smith 



The Phylloxera 



In the report to the Department of the Interior of the Canton 

 of Geneva by the commission appointed to inquire into the 

 best means of stopping the ravages of Phylloxera, which I have 

 just received from Prof. Foiel, of Morges, it is stated that the 

 insect was most probably introduced from England in some vines 

 which were taken to Geneva to certain graperies of Baron Roth- 

 schild in i86g. These graperies are in the middle of the infected 

 district — they were found to be infected within twelve months 

 of the arrival of the plants, and no vineyards but those in the 

 neighbourhood of these grap<;ries have been infected in all 

 Switzerland. Prof. Forel, in his letter to me, says that while the 

 surrounding vines have perished, tho^e attacked in B.iron Roth- 

 schild's houses have suffered very'little indeed, and bear plenty of 

 fruit. These vines, he says, are Black Hamburgh and Muscat 

 d'Alexandric or d'Alicante. He asks if in England anything is 

 known which points out any kind of vine as suffering less than 

 other kinds. Can any of your readers tell me anything about it? 



Chfton, Jan. 23 "^ " w.>, , .c.r„„ 



G. H. WrjLLASTON 



Thermometer Scales 



I SHALL feel greatly obligid if any reader of Nature can 

 inform me what scale the thermometer referred to in the follow- 

 ing extracts was made to :— " 7 Feb., 1775. This day the ther- 

 mometer was down to So, two hours after sunrise." "This 

 thermometer has five inches divided into 75 degrees above tem- 

 perate {sic) ; and 6!} inches below temperate, divided into 

 100 degrees ; the spirit at 80 was about an inch from the bottom. 

 In the frost in 1739 the spirit sunk below all the marks in this 

 thermometer." Abo— " Dec. 30, 1739. Thermometer sunk 

 below all the marks. . . . This thermo was marked down to 7 

 below Fahrenheit's freezing point of 32 : so this was below 25 

 of Fahr." Some very hot days in July 1757 are marked (I pre- 

 sume by the same thermometer) at 40, 41, 46. and 47 degrees; 

 another day, "very near 50" is spoken ot as the hottest day the 

 writer thinks he ever remembers in England, "except the famous 

 hot Saturday on the nth of June, 174S." 



In 17S3-4, 13 below o of Liini,riis is mentioned as very severe 

 cold. The scale of Linnaeus is mentioned several times. I have 

 failed to discover the scale of the first thermometer, and never 

 heard of that of Linnreus. If any of your readers can enlighten 

 me as to the relation of these scales to that of Fahrenheit or 

 Reaumur, I shall feel greatly indebted. 



Norwich, Feb. i THOMAS Southwell 



OUR ASTRONOMICAL COLUMN 

 The next return of Halley's COMET.--In the 

 year 1864 the late Count G. de Pontdcoulant made an 

 important communication to the Paris Academy of 



Sciences relating to the perturbations of this famous 

 comet. He remarked at the outset : " I propose, in my 

 new researches on the comet of Halley, to foUov/ the 

 course of that body from the epoch when it was observed 

 for the first time in a manner sufficiently precise to allow 

 of determining the orbit, until that of its next return to 

 perihelion, which will take place in 1910, i.c\ during an 

 interval of nearly three hundred and eighty years, in- 

 cluding five entire revolutions of the comet. I shall 

 describe here, as succinctly as it is possible to do, the 

 results of the immense calculations which it has been 

 necessary to effect in order to attain this object." We 

 shall confine ourselves in the present remarks to a few 

 particulars relating to the appearance of the comet in 

 1910, reserving a further account of Pontdcoulant's 

 memoir for a future occasion. It is, however, impossi'ole 

 to avoid an expression of regret that the astronomer who 

 has completed the enormous work indicated in the above 

 extract, should have passed away without (so far as we 

 know) putting upon record the successive steps of his 

 calculations in sufficient detail to be of service to the 

 future investigator, and it is to be hoped his papers may 

 yet be made available for this purpose. Mere statements 

 of final results, necessitating for their attainment such a 

 prodigious amount of labour and such unusual skill, are 

 hardly all that is required, though in this remark we imply 

 no want of confidence iit the accuracy of the work per- 

 formed. It is almost certain that the perturbations of 

 Halle>'s comet will be recomputed before the year of its 

 next return, and it is as certain that the possession in 

 detail of the various numerical results of Pontccoulant's 

 work would be of very great service to anyone who may 

 undertake its verification, not only by way of check as he 

 proceeds, but as a guide to the effective management of 

 the formidable mass of figures involved. 



The perihelion passage in 1S35 is fixed to Nov. I5'95 

 Paris mean time, at which moment the comet is found to 

 have been moving in an ellipse with a period of 27895"Si 

 days. The influence of the p'anet Jupiter upon the length 

 of the present revolution is greater than in any of the four 

 previous ones, and am.ounts to 6ycj'27 days, by which the 

 next perilielion passage is accelerated. Saturn retards 

 the comet 279 days, while Uranus accelerates it 2'30 

 days, therefore nearly negativing the infiu^nce of Saturn. 

 The attraction of other plane's is neglected. The total 

 effect of perturbation during the actual revolution is thus 

 found to be 67888 days, the period being shortened 

 thereby ; and hence the time of revolution corresponding 

 to 1S35, Nov. 16, is diminished to 272i6'93 days, and the 

 next perihelion passage is consequently fixed to 1910, 

 May, 23S7 Paris time, the comet then completing the 

 shortest revolution since 1531, the preceding revolution 

 having been the longest, and their difference is upwards 

 of two years. The periodic time corresponding to the 

 comet's motion at perihelion in 1910 is 27,790 days. A 

 notable change is produced by the action of the planet 

 Jupiter in the perihelion distance, which is increased by 

 upwards of a tenth of the earth's mean distance from the 

 sun, and the comet's orbit is thus brought into very close 

 proximity to that of the earth at the descending node. 

 In 1S35 the comet at this point passed o'i5ii from our 

 track ; in 1910, according to Pontccoulant, it will be 

 distant only o'Oi57. The excentricity of the orbit in 1910 

 is found to be o'96i7332 ; the semi-axis major, I7'95S46 ; 

 the longitude of perihelion, 305° 38' 14" ; the ascending 

 node, 57° 10' 33"; inclination, 17° 46' 51" ; the motion is 

 retrograde. The longitudes are counted from the mean 

 equinox at perihelion. 



The track of the comet calculated from these elements 

 is a very favourable one for observation. At the end of 

 October 1909 the comet has the same theoretical inten- 

 sity of light as when it was last glimpsed by Dr. Lamont 

 with the Munich refractor, on the 17th of May, 1836. (It 

 is often erroneously supposed that the last observations 



