i6o 



KNOWLEDGE ^: SCIENTIFIC NEWS. 



[Jul 



1905. 



PHYSICAL. 



By Alfrel) W. Porter, B.Sc. 



Ether Drift. 



The question as to whether or not the earth carries the 

 ctlur near it in its journey through space is one of very great 

 theoretical importance, and the last word upon it has not yet 

 been said. The fact that stellar aberration has the same value 

 whether determined by means of an ordinary telescope or by 

 one filled with water can most simply be explained by sup- 

 posing that in the xiuter the ether is carried forward with a 

 portion only of the earth's velocity, while in the air round the 

 telescope it is sensibly at rest in space. 



On the other hand, the results of Michelson's and Morley's 

 experiments with their interferometer can be accounted for 

 most simply by supposing that both the earth and the ether 

 near it are moving with the same speed; that is to say, that 

 the earth drags the surrounding ether with it in much the 

 same way as that by which a layer of air is carried by a pro- 

 jectile. 



Experiments by Sir O. Lodge on whirling massive discs 

 prove that they at any rate exert no perceptible drag ; and. 

 consequently, if the earth does so, it must be due to its great 

 magnitude. It was pointed out by FitzGerald (and inde- 

 pendently by Loreotz) that if we suppose that the length of a 

 body when set moving is shortened in the direction of that 

 motion then Michelson and Morley's experiments do not 

 imply the absence of relative motion ; in fact, if the shortening 

 takes place to an appropriate extent, they do not show that 

 the ether is moved at all. Other experiments have also been 

 made which seem to require that this supposed shortening is 

 real. 



Morley has recently {Philosophical Magazine, May, 1905) 

 varied his previous investigation with the object of testing 

 whether the compensation which cancels the effect due to 

 relative motion is complete in ever>' case. It is the shrinkage 

 of the base plate of his apparatus which may come into 

 play; and, besides improving the apparatus by increasing the 

 sensitiveness, he has changed the material of this plate from 

 iron to wood. There is still absence of any indication of 

 relative motion of earth and ether, and the proportional 

 shortening must therefore be the same as in the previous 

 experiments. 



It may at first sight seem unlikely that two such different 

 materials should be equally affected. But the true explana- 

 tion must be that it is not the nature of the molecule (or 

 molecular aggregate) or even that of the chemical atom which 

 determines it ; for these are v'cry different in the two cases. 

 It is something more fine grained than these, and this some- 

 thing must be essentially identical (at any rate as far as this 

 particular property goes) in both these bodies. In fact, the 

 result is an additional piece ot evidence in favour of the 

 theory that all atoms are built up of smaller particles, each 

 one of which is of the same kind. 



A New Interrupter. 



Workers with induction coils know too well the trouble 

 there is with the interrupter, whatever its type. The difficulty 

 is to a very large extent removed in the Grisson Resonance 

 Apparatus which is put on the market by Messrs. Isenthal 

 ana Co. The intermittence of the current in the primary 

 coil is produced by means of a modified commutator which 

 is spun round by a :}H. P. electric motor. The commutator 

 interchanges, with a frequency up to 200 times a second, the 

 connections of the armatures of a condenser with the primary 

 coil and battery (or nfhrr ';nirlirectional source) which are in 

 series with it. .\' 1I the battery sends through the 



coil a quantity i:qual to twice the maximum 



charge of the c.i : these impul.scs must always go 



the same way throuj;h th'j primary. Since the current into 

 the condenser rises ver>- fast (owing to the small inductance of 

 the primary) and then falls off much more gradually, the quan- 

 tity that flows through the secondary is nearly, if not perfectly, 

 unidirectional and hence is suitalile for exciting .\-ray bulbs. 

 The essential reason of the efficiency of the commutation 

 arises from the fact that the reversal takes place when the 

 current into the condenser is zero, or at any rate very small ; 



in consequence there is absolutely no visible sparking at it. 

 This is the case through the whole working range of speed, for 

 it is at most the tail end only of the flow th-it is cut off. 



Instead of commutating the condenser it may be the battery 

 that is so treated. The flow through the primary is then 

 alternately of opposite .signs, and the flow through the 

 secondary is also alternating. In this case by suitably choos- 

 ing the inductances, the condition of resonance mav be set 

 up at particular .speeds. In fact, by this means from the 

 primary circuit alone, an c.m.f. of much higher than 100 volts 

 can be obtained by the use of a 100-volt circuit. 



The condensers employed are electrolytic condensers consist- 

 ing of aluminium plates immersed in an electrolyte contained 

 in a seamless steel vessel. Iiach of these is capable of furnish- 

 ing a current of 15 amperes from a :io-volt lighting circuit. 

 Greater currents can be obtained by connecting a number in 

 parallel. Such condensers arc very comp.ict, the dielectric 

 being the thin film of aluminium oxide which forms on the 

 plates. 



When the coil is replaced by a suitably wound electro- 

 magnet a powerful alternating magnetic field is produced 

 which acts on the nervous system. If the forehead is placed 

 close to one of its poles a flickering sensation of light is 

 experienced. 



The spinning commutator is made in a thoroughly work- 

 manlike way ; its design is of an engineering type contrary to 

 what is only too frequently turned out by instrument makers. 



ZOOLOGICAL. 



By R. Lydekker. 



The Smallest British Dinosaur. 



The Dinosauri.in reptiles — both small and gic.it — appear to 

 be attracting a considerable amount of attention at the present 

 time. One of the latest contributions to the literature of the 

 subject is a note in the May number of the Gcoh>f;ical Ma-^azine, 

 by Baron Francis Nopcsa, on the skull of llyf>silof>hotioit, a 

 species from the Wealden of the Isle of Wight, of about the 

 size of a fox. ana it not actually the most diminutive, at all 

 events one of the smallest representatives of the group. De- 

 spite its diminutive size, it appears to have walked on its hind 

 legs after the fashion of its gigantic cousin, the iguanodon, of 

 the same epoch. In a specimen preserved in the British 

 Museum, Baron Nopcsa shows that what had been taken for 

 the skull of the creature is really its lower jaw, and that the 

 structures described as bony plates from the white of the eye 

 are really the teeth. Consequently, there is every reason to 

 believe that all dinosaurs, like their relatives, the crocodiles, 

 lacked a ring of bony plates in the white of the eye. 



The English Wa-ter-Shrew. 



Captain Barrett-Hamilton, in a recent issue of the Annals 

 and MaKazinc of Xaltiial History, points out that the British 

 representative of the water-shrew differs from the typical con- 

 tinental form of that animal to an extent sufficient to permit 

 it to rank as a distinct local race, for which the name Scomys 

 foiliens ciliatiis is available. There are likewise several 

 continental races of the species, the Scandinavian, ^nd other 

 mountain forms, in common with the one from the British 

 Islands, being dull-coloured creatures, in comparison with 

 those inhabiting the lowlands. 



Fa.ce-gland Vestiges in the Horse. 



In a paper published in the May nuiiibei- of the .\iiiiiih and 

 Maijazinc of .Wilunil History, Mr. R. I. I'oeock considers that 

 the depression so frequently found in the skulls of Arab 

 horses and thoroughbreds, immediately in front of the eye, has 

 nothing to do with the face-gland of the extinct hipparions, 

 but is merely for muscular attachment. If this be so, the 

 theory as to the importance of this depression in regard to 

 to the origin of Arabs and tlioroughbreds is wiped out at one 

 stroke. Despite the fact that the existence of functional 

 face-glands has been recorded in two living horses, the author 

 considers himself justified in stating that the modern horse 

 nc\'er exhibits any trace of the hipp.-irion's f.ice-gland. 



