230 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Sept., 1905. 



proportional to the extension o{ the spring. Mr. Lanchester 



prefers the easier method of arranging the mass as the bob of 

 a pendulum. This pendulum becomes deflected whenever 

 the point of support receives an acceleration, and from the 

 angle of deflection the acceleration is determined ; in fact, the 

 horizontal acceleration bears to that of gravitj- a ratio equal to 

 the tangent of the deflection. The first instrument of this kind 

 was made by him in 18S9. In the 1904 model an improvement 

 has been effected in the mode of automatically recordinsr the 

 acceleration. Since this quantity is proportional to the tangent 

 of the deflection, the recording pencil must be so arranged as 

 to move equal distances for equal increments of deflection. 

 This result is attained by pivotting the pencil arm to the 

 pendulum continuation in such a manner that the point of the 

 pencil lies always in the plane of the pendulum axis. It is 

 assumed in the theor>' of the instrument that the motion of the 

 pendulum bob is substantially that of the rest of the vehicle, 

 and consequently its motion of swing should be negligible in 

 comparison with the motion of the vehicle. Its time of swing 

 must also be kept small compared with the time of change of 

 acceleration which it is required to record. This necessitates 

 the use of a ver>' short pendulum, which in the later model is 

 reduced to 1:5 inches. .An oil dash pot is employed to make 

 the movements deadbeat. A characteristic feature of 

 diagrams taken by means of this instrument is the sud- 

 denness of the drop at the instant of stopping. This re- 

 presents the jerk nearly always experienced just as a train 

 comes to rest. A jerk consists in fact of a very sudden change 

 in acceleration, and not of a large acceleration. Mr. Lan- 

 chester suggests that the term " jerk " might be given a 

 scientific meaning by defining if as the rate of change of 

 acceleration. To prevent this jerk the brake of a vehicle 

 should be taken nearly off before completely stopping. For 

 further information the reader is referred to the Pliilcsophical 

 Magazine for .-\ugust. 



The Methods of Physics. 



In mathematical physics we employ two kinds of theories, 

 which may both lead to an understanding to a certain extent 

 of what goes on in the material world, and which are neverthe- 

 less very different in their nature and in the aims which they 

 declare. In the theories of the first kind, it is sought to pene- 

 trate the intimate mechanism of phenomena; we endeavour 

 to represent the motion of molecules and atoms, and, as one 

 must now add, also of ions and electrons; we determine their 

 velocities and dimensions, the masses and electric charges of 

 these extremely small particles. All this is foreign to theories 

 of the second kind. Physicists who prefer these concern 

 themselves only with magnitudes which are accessible directly 

 to our observations, such as temperatures, quantities of heat, 

 electric currents, &c. After having measured these magni- 

 tudes they establish their mutual relations, and show that 

 these relations are in accordance with certain general prin- 

 ciples, amongst which the law of the conservation of energy 

 and the second law of thermodynamics are the most impor- 

 tant.^ — H. A. Loreniz, La Thermodynamique et les theories 

 cineliqncs {Journal de Pliysii/iif, August, 1905). 



ZOOLOGICAL. 



P.y K. LVDEKKFIR. 



The Lower Jaw of Manrimals. 



Hitherto it has been generally supposed that the lower 

 jaw of mammals differs fundamentally from that of birds and 

 reptiles in that each lateral half is formed of a single piece, 

 instead of comprising a number of distinct elements. Accord- 

 ing, however, to recent investigations on the jaws of embryos 

 undertaken by Professor Carl von Bardeleben, this is a 

 mistaken idea, and in the young condition the mammalian 

 jaw shows the same compound structure as that of a bird or 

 a reptile. The mammalian jaw is indeed now stated to be 

 strictly comparable in every detail with that of a reptile. 



Mammal or Reptile? 



.\ fossil skull from the Karoo system of South Africa 

 described in 1884 by Sir R. Owen as that of a mammal, under 

 the name of Triiy Union longtti'tis, was subsequently assigned 

 by Professor H. G. Seeley to the reptilian class. Recently 

 Dr. R. Broom, in the Transactions of the South African 

 Philosophical Society, has again pronounced in favour of 

 the mammalian nature of the fossil. Taking all points into 

 consideration, the author believes Tritylodon to be a mammal, 

 whose nearest affinities are with the egg-laying duckbill and 

 spiny anteaters of Australasia, which are evidently specialised 

 survivors of a once abundant primitive group. Perhaps the 

 real truth is that the South African fossil presents so many 

 resemblances to manunals on the one hand and to reptiles on 

 the other, that it can scarcely be assigned to either group, 

 but rather forms a connecting link between the two. 



A British Armoured Dinosaur. 



Not long aj,'!! reference was madr to recent investigations 

 into the structure of the small dinosaur from the Wealden of 

 the Isle of Wight, known as IlypsilopluHlim fo.xi. The same 

 energetic investigator, I5aron Francis Nopcsa, has published 

 in the June number of the Geoloj^ical Magazine an account of 

 another dinosaurian reptile, Polacanllnis fo.xi. from the same 

 locality and formation. The restoration shows a long-bodied 

 reptile of about three feet in height at the shoulder, with the 

 hind-quarters invested in a solid bony shield, and the upper 

 surface of the rest of the body, the neck, and the tail pro- 

 tected by a double row of large bony plates standing 

 vertically. The creature may in fact be regarded as a kind 

 of reptilian armadillo. It may be mentioned that the author 

 takes no notice of the fact that the name Polacanthiis is pre- 

 occupied by the designation applied to the paradise-fish 

 iPolyacuntJiiis). 



R.eptlles from North Greenland. 



As aflbrding additional confirmation to the idea that the 

 Arctic regions once enjoyed a genial climate, considerable 

 interest attaches to the description by Dr. V.. Fraas, in 

 Midiidchcr om Gyonlands, of reptilian remains from the Jurassic 

 strata of Northern (ireenland. The first of these is the foot- 

 print of a land dinosaur, while the second is a vertebra of one 

 of the ichthyosaurs, or fish-lizards. It seems, therefore, that 

 in Jurassic times the polar ocean was entirely Tree from ice. 



An Extinct Sea-Lion. 



Very little is known as to the past history of the sea-lions 

 and sea-bears (fur-seals), and it is, therefore, a matter for 

 congratulation that a fine skull has been obtained recently 

 from the Miocene strata of ( )regon. Mr. F. W. True, who has 

 described the specimen, states that it is considerably larger 

 than any existing sea-lion skull that has come under his notice, 

 its basal length when entire being probably about twenty 

 inches. The new name, Pontolian nuignns, is proposed for the 

 fossil sea-lion, as the characters of the skull and teeth do not 

 agree precisely with those of any living member of the group. 

 It should be mentioned, however, that if all the modern eared 

 seals are included in the single genus Olaria, as is still the 

 practice with some zoologists, there would apparently be no 

 reason to exclude the fossil species. 



The Black Sea Porpoise. 



According to the well-known student of the Cctacea, 

 Dr. O. Abel, the porpoise of the HIack Sea is quite distinct 

 from the common porpoise of the Atlantic (Plioc/inn com- 

 ninnin), the < hief difference being apparently the form of the 

 head. PDr this species the name Phocana rrlicin is proposed. 

 Seeing that the common porpoise does not enter the Mediter- 

 ranean, it is only natural to expect that its Fuxine representa- 

 tive .should be distinct. Dr. Abel considers that the reason 

 why porpoises do not enter the Mediterranean is because the 

 water is too salt for them. In the same comnnmication he 

 describes a fossil porpoise-skull from the Miocene- strata of the 

 Taman Peninsula as Pnlirobhocuna, regarding it as represent- 

 ing an ancestral member of the group. 



