62 



NATURE 



[May 1 8, 1893 



periodic comets due this year. The following is a search ephe- 

 meris for the present month for intervals of four days ; — 



1393. R.A. Decl. 



h. m. s. o / 



May 20 ... 23 48 12 ... -4 24 



24 ... o s 24 ... -2 34 



28 .. o 22 57 ... -o 40 



June I ... o 40 53 ... + 1 16 



L'Astronomie FOR May. — This number commences with the 

 •discourses delivered by M. Tisserand and M. Flammarion before 

 the Astronomical Society of France, the former " On the Pro- 

 gress of Astronomy durin:; the Past Year, " and the latter "On 

 the Pr,)gre5s of the .Society itself. — A brief but interesting 

 articlefrom the pen of Dr. Lorin, on "Celestial Photography," 

 will be of special value to possessors of small instruments, since he 

 shows how they can be adaptedfor thetakingof such photographs. 

 "With reference to the late solar eclipse, several observatories 

 have communicated their observations as mide on the Continent, 

 accompanying them with drawings, which are here inserted. 



The Lunar Atmosphere. — At the Observatory of Alger, 

 M. Spee {Camples Rendus, April 24, No. 17) made some in- 

 teresting observations to find out whether any modifications 

 ■due to a lunar atmosphere were produced in the lines of the 

 solar spectrum (i) in the neighbourhood of the horns, and (2) 

 at the point of contact of the lunar disc with a sun-spot. The 

 observations, he says, were made under the best conditions, but 

 j;ave a negative answer to the first of these two investigations. 

 With regard to the second he says that no change was noted 

 tintil at the moment of the greatest phase when the lines of 

 magnesium ^' b'^ b* "appeared sharp and seemed to be ac- 

 companied on both sides with very fine lines reminding one of 

 what in spectroscopy is known under the name of persiennes. 

 C was terminated, as M. Spee says, " en fer de /aHCi! " penetra- 

 ting the chromosphere. 



Bulletin Astronomique for April. — In this periodical 

 for the past month M. Haerdtl contributes some notes relative 

 to some small inequalities of long period in the movements of 

 the Moon, Earth, and Mars. The determination of the orbit 

 of the periodical comet Finlay (1886 vii.) is the subject of a long 

 article by M. Schulhof, but in this (to be continued in the next) 

 he only limits himself to the ephemeris and the mean positions 

 of the comparison stars, with copious notes giving the authori- 

 ties, proper movements, and remarks. Apropos of the question 

 of the variation of latitudes M. Boquet gives an interesting 

 historical notice on the latitude of the Observatory of Paris, in 

 which he recapitulates all the attempts made to fif the value of 

 this important element. Now that we know that variations 

 occur, it is most interesting to read the remarks of the authors 

 of these various determinations at different times with respect 

 to the discrepancies between the values. M. Yvon Villarceau 

 for instance, from his observations in i865 and 1867 says : 

 " Quant a la mesure exacte de la latitude, nous ne voyons pas 

 qu'elle puisse resulter des mesures faites aux Cercles muraux de 

 Gambey et de Fordin." .... 



GEOGRAPHICAL NOTES. 



The death of Mr. W. Cotton Oswell on May It, at the age 

 of 75, removed a famous African traveller and hunter whose name 

 had almost ceased to be remembered by the general public. In 

 his early life Mr. Oswell spent five years in South Africa hunting 

 and exploring. His adventures were of the most thrilling kind, 

 and the trophies he preserved in his house at Groombridgeform 

 a unique collection. He was associated with Livingstone in 

 his earlier travels, and chained himself with the care of 

 the waggons and the provision of food, while his com- 

 panion planned the route and made scientific observations. In 

 this way Mr. Oswell was with Livingstone at the discovery of 

 Lake Ngami. Subsequently Mr. Oswell travelled and made 

 collections in South America and elsewhere, but his extreme 

 modesty prevented him from thrustinghimself before the public, 

 and he wrote nothing. His geniality in private life was as re- 

 markable a feature of his character as his shrinking from all 

 public appearances. 



The Canadian Government has decided to despatch an ex- 

 pedition, under the charge of Mr. J. B. Tyrrell, of the Geologi- 

 cal Survey of Canada, to explore the barren ground northward 

 from Lake Athabasca, a region which has not been visited by 

 tomieient observers since 1772. 



NO. 1229, VOL. 48] 



M. Marcel Dubois has been appointed to the Chair of 

 Colonial Geography, the foundation of which at the Sorbonne 

 we intimated last year. 



The higher teaching of geography in England is not confined 

 to the lectures delivered at the two ancient Universities. For 

 some years Prof. C. Lapworth, F.R.S., has given courses on 

 physical and political geography at the Mason College, Birming- 

 ham, which are this session attended by over eighty students. 

 The complete course occupies two years, lectures being given 

 twice a week ; the syllabus is drawn out on thoroughly scientific 

 lines, and while entirely original in treatment is comparable 

 with the best instruction given in the same subject in German 

 Universities. 



Engineering works of such magnitude as to be of geograph- 

 ical importance have been for some time carried out on the 

 Alsatian slope of the Vosges in order to regulate the water supply 

 for industrial purposes. A series of reservoirs, so large as to be 

 described as artificial lakes, has thus been formed, and the rain- 

 fall of the district can now be utilised much more completely 

 than was formerly possible. 



THE FUNDAMENTAL AXIOMS OF 

 DYNAMICS. 

 T N view of a discussion at the Physical Society of London on 

 -"■ Friday, the 26th inst., it may be convenient if I anticipate 

 future communications so far as to give in a brief or summary 

 form the "Laws of Motion " simewhat as I propose to advocate 

 their acceptance ; not, however, entering into details, and not 

 being specially careful about precise form of words, rather aim- 

 ing at giving the general sense with the object of assisting dis- 

 cussion by abbreviating or summarising my paper in a few definite 

 statements. 



Notions derived more or less directly from sensations, and 

 here accepted as understood without special definition. 



Motion, Space (extent and direction). Velocity (including 

 direction), Time, Stress, Force (including direction), Matter. 



About all these there is much to say ; some are more im- 

 mediate sense-perceptions than others, but a detailed discussion 

 of them verges on metaphysic-, and is not an essential pre- 

 liminary to a physical treatise. All that is necessary is 

 explanation and illustration sufficient to render the terms intel- 

 ligible. All that I shall say here is that by "matter" is 

 meant primarily somettiing tangible or resisting ; that we 

 experience "force" when we push a truck; that a thumb- 

 screw gives us a notion of " stress " : and that pushing a truck 

 does also, if we attend to both hands and feet. 



Remarks, Practical Assumptions, and Experiments. 



There is no need to discriminate a force from a vector in a 

 fundamental treatment, because all ideas about moment of force, 

 angular momentum, and the like, belong to a consideration of 

 the behaviour of a rigid body, which is an artificial agglomera- 

 tion of connected particles : convenient, not fundamental. 



But there are some assumptions and experiments needful to 

 l)e made concerning the measurement of force more precisely 

 than by our muscles. 



{Assumption i). That the weight of a given piece of matter at 

 a given place is not liable to capricious change. 



{Assumpiion 2). That two similar lumps of matter weigh twice 

 as much as either. 



{Experimental result 1). That strains of elastic bodies are 

 proportional to the stresses within certain limits. 



{Experimental result 2). That the frequency of a loaded 

 elastic body, vibrating within the above limits is independent of 

 amplitude. 



{txperimental result 3). That in cases of impact there is one 

 point whose motion is undisturbed by the blow. 



Definition r, Simple Experiences, and Axioms, 



{Experience l). A stress consists of two forces. 



{Definition 1). Acceleration (including direction) = dv/r//. • 



{Experience 2). Acceleration occurs in matter subject to an 

 unbalanced force. 



{Axiom I). Without force there can be no acceleration of 

 matter. 



{Experience 3). The acceleration appears to agree with the 

 force in direction, and is in some cases demonstrably propor- 

 tional to the force. (A deduction from experimental result 2 

 above.) 



