28 



NA TURE 



[November 9, 1899 



is to be remarked that the efficacy of the course he lays 

 •down must depend very largely on the adjustment to it 

 of lecture and tutorial instruction. How successfully 

 this difficulty has been met in the University of Chicago 

 -we have not the means of judging. The book as it 

 stands leaves the reader under the necessity of con- 

 structing in imagination the whole course of lectures or 

 preferably " conferences " to which it is essentially 

 related, and it is hardly likely to be put in use by 

 English teachers unless they are prepared to recast their 

 oral teaching to suit it. 



The particular order in which the topics of general 

 chemistry are to be treated, the particular points to be 

 elucidated by the student's own experiments, are matters 

 which may afford room for endless choice, but after that, 

 in the point of method, there is a clearer right and wrong 

 to choose between. We believe that some chemists 

 may take exception to Dr. Smith's order and choice of 

 topics, but his method of bringing them before the 

 student will probably meet with general approval. He 

 strives throughout to cultivate the investigator's attitude 

 of mind, bearing in mind however that it is impracticable 

 for the laboratory training of a chemist to be wholly 

 carried out on this plan. The text is interspersed with 

 question marks and with parenthetical injunctions to the 

 student to interpret and correlate his facts. 



The exercises are all drawn from inorganic and 

 fphysical chemistry, and include an elementary study 

 of the cardinal points of theory. We can well believe 

 that this course of practical work, combined with 

 properly conducted class meetings, will furnish a 

 much more effectual introduction to the study of 

 chemistry than students ordinarily obtain in Universities, 

 where the continuous expository lecture to junior classes, 

 junlimited in size and containing all sorts and conditions 

 of students, is still the customary, if not the inevitable, 

 method of procedure. A. S, 



Ueber den Habitus der Coniferen. Von Dr. A. H. 



Burt. Pp.86. (Tubingen: Verlag von Franz Pietzcker, 

 - 1899.) 



This inaugural dissertation is mainly concerned with an 

 analysis of the forms exhibited by the different groups 

 of conifers. Following Vochtung, the author recognises 

 two principal types — the monocormic and polycormic 

 respectively. The former is characterised by the presence 

 of a decided main axis, the lateral axes being dominated 

 by its growth ; the common spruce fir is an example of 

 a monocormic conifer. Polycormic forms are met with 

 in cypresses and junipers, in which the lateral branches 

 are not all reduced to subordinate and graduated 

 positions ; whilst in the cedars, forms are met with 

 which combine the characters of both of the principal 

 types. 



Elaborate tables of measurements of the relative 

 lengths of main and lateral shoots, and of the angles 

 made by them, are given in the text, and clearly bring 

 out the factors on which the shapes of conifers depend. 

 Beasts: Thumb-nail Studies, in Pets. By Wardlaw 



Kennedy. Pp. xvi + 152. (London : Macmillan and 



Co., Ltd., 1899.) 

 The spirit of a true naturalist prevails throughout this 

 book. The author records his experiences with a number 

 of uncommon animal pets, among which were a young 

 crocodile, a python, an armadillo, and a mongoose. His 

 observations are of real scientific interest, and his 

 humorous descriptions are pleasant to read as well as in- 

 structive. Though natural history cannot be learnt from 

 books, the boy who reads the essays in this volume will be 

 encouraged to observe the habits of animals for himself, 

 and will thus learn to depend upon the evidence of his 

 senses rather than to trust upon second-hand inform- 

 ation. The book would be an acceptable Christmas 

 present for any boy interested in natural history. 



NO. 1567, VOL. 6l] 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications .\ 



Next Week's Leonid Shower. 



The anticipated return of the great Leonid shower within a 

 few days is looked forward to with so much interest that it 

 appears desirable to examine what data we possess for forming 

 a forecast in relation to it. 



In a paper on the perturbations of the Leonids, which is 

 published in the Proceedings of the Royal Society for March 2, 

 1899, we gave the perturbations which have during the last 

 thirty-three years affected those meteors which are situated 

 near a particular station in the stream, namely the station 

 through which the earth passed in 1866 and of which Adams 

 had computed the orbit. It will be convenient to speak of this 

 position in the immensely long stream of ortho-Leonids as 

 station A. 



By these calculations it was ascertained that this portion of 

 the stream has been subjected to an unusual amount of perturb- 

 ation during the revolution which has occupied the last thirty- 

 three and a quarter years ; so much so, that the advance of the 

 node, upon which the epoch of the coming shower largely 

 depends, has during this revolution been of more than three 

 and a half times its average amount. Its having had this 

 exceptional value has been caused by unusually close approaches 

 of the great planets Jupiter and Saturn to the meteors during 

 this revolution. 



Another effect of these abnormal perturbations has been to 

 shift the position of the ellipse in which station A moves in a 

 direction perpendicular to the earth's path, so that the point in 

 which it pierces the plane of the ecliptic will, on the 15th of 

 the present month, lie inside the earth's orbit at a distance from 

 it of o*oi4i of the earth's mean distance from the sun. This 

 would be a sufficiently large displacement to carry the stream 

 entirely clear of the earth, if it were a mere cylindrical stream ; 

 in which case we should have no great shower this year. But we 

 have satisfied ourselves, by an examination made by one of us 

 into the dynamical conditions which prevailed when the 

 Leonids were drawn by the planet Uranus into the solar 

 system, that the stream is not thread-like but strap-shaped, so 

 that its intersection with the plane of the ecliptic is an oval of 

 some sort — probably a long oval — of which the longer axis 

 originally lay nearly perpendicular to the earth's path. On 

 account of this oval form of the section of the stream, the 

 earth is likely to receive one of the great showers this year, 

 notwithstanding the fact that the situation in the stream through 

 which the earth passed in 1866, will on its return pass at some 

 distance from the earth. 



If the longer axis of the oval now lay perpendicular to the 

 earth's path, the most probable epoch for the middle of the 

 shower of this year would be 1899 November I5d. i8h., which 

 epoch we offered with careful reservations in the paper which is 

 above cited. A further examination, however, has shown us 

 that perturbations have been acting on this oval ever since the 

 Leonids became members of the solar system, tending very 

 slowly to rotate its major axis in a retrograde direction through 

 an angle which will ultimately become nearly a right angle. The 

 data at our disposal do not enable us to compute how far 

 this retrogade shift has carried the axis in the seventeen 

 centuries during which perturbating forces have been acting 

 upon it. Under these circumstances we must have recourse to 

 observation to ascertain the amount of the shift. A laborious 

 attempt to estimate it in this way has furnished 52° as the angle of 

 shift, which would indicate that the epoch for the shower of this 

 year is as much as twenty-two hours earlier than 1899 

 November I5d. i8h., that is it would bring it back to 1899 

 November I4d. 20h ; but we do not attach any value to this 

 particular determination, inasmuch as the data which are as yet 

 at our disposal are too uncertain for us to rely on them. What 

 appears tolerably certain is that so?ne shift of the position of the 

 oval section of the stream has taken place, and that the middle 

 of the shower is accordingly likely to come earlier than 1899 

 November I5d. l8h., probably some hours earlier, and possibly 

 a considerable number of hours. Under these circumstances it 

 appears desirable that a watch shall be maintained in the atter 



