January 17, 19 18] 



NATURE 



395 



of the species are printed on a large chart adjacent to 

 the stations at which they were collected. Prof. Hick- 

 son directs attention to the rich harvest of sea-pens 

 gathered around Amboyna, the Banda and Kei Islands, 

 and off the south coast of Timor and Flores, and 

 concludes that the Malayan region is the headquarters 

 of the genera Pteroeides and Virgularia. He remarks 

 that, although there is not sufficient information in 

 regard to other genera to justify a similar conclusion, 

 the facts as they stand are in accordance with the 

 view that the Malay Archipelago is, or has been, a 

 distributing centre of the Pennatulacea of the world. 

 Of special interest from the point of view of geo- 

 graphical distribution is the occurrence of the fol- 

 lowmg, all deep-sea forms : Chunejla gracillima, 

 previously known from the east coast of Africa ; the 

 genus Gyrophyllum, hitherto recorded only from the 

 North Atlantic; and five sf>ecies of Umbellula. 



Anatomical and histological investigations have been 

 made on a number of interesting points, e.g. (i) the 

 ciliated radial canals, found throughout the rachis of 

 Virgularia, which Prof. Hickson suggests are con- 

 cerned with the flow of water into and distension of 

 the colony ; (ii) the large mesozooids of Pennatula 

 murrayi, the structure of which indicates that they 

 bring about rapid expulsion of water from the prin- 

 cipal canals; (iii) the brown ciliated tubes of this 

 species ; and (iv) the gonads — all the sf>ecies examined 

 proved to be dioecious and oviparous. 



Useful keys are given to the families, genera, and 

 species, and the memoir is illustrated by ten plates 

 and fortv-five text-figures 



Prof. Hickson is to be warmly congratulated on the 

 completion of this important memoir, which is charac- 

 terised throughout by great care and sound judgment. 



EXPERIMENTAL HYDRAULICS.^ 



THE small amount of evidence, which many 

 engineers are willing to accept as satisfactory 

 proof of some principle or empiricism used in con- 

 ^lection with their designing, is sometimes surprising 

 to those who combine, with engineering experience, 

 knowledge of the more refined and rigid methods of 

 scientific inquiry. Perhaps there is no more striking 

 evidence of this than in connection with the formulae 

 used by engineers, in perfect faith, to determine the 

 flow of water over weirs and through orifices and 

 nozzles. 



Very frequently in experimental work there is a 

 want of precision in the results, owing to lack of 

 appreciation of what might be called the persistence 

 of hydraulic disturbance. In our technical colleges 

 apparatus which is supposed to compare the loss of 

 head in certain lengths of pipes of different form, and 

 certainly measures something, but not that which the 

 designer intended, is not infrequently used by students. 



It is to be regretted that so little attention has been 

 paid in this country to precise experimental hydraulics ; 

 but because of that we are so much the more indebted to 

 those workers who, in France and the United States, 

 have added to our experimental knowledge of this 

 important subject. 



Tlie modern universities of the United States are 

 issuing from their experimental stations many interest- 

 ing Bulletins describing the results of special re- 

 siearches, and Bulletin 96 of the University of Illi- 

 nois, though not by any means ambitious, is yet of 

 sufficient importance to receive a passing notice in the 

 columns of Nature. It describes experiments on the 

 effect of fixing mouthpieces of different shapes on a dis- 



1 "The Kff.Ttof Mouthoieres on the Flow of Water throuifh a Sub- 

 merged Short Pipe." By F. B. Seely. Bulletin No. 96. (University of 

 Il'inois.) 



NO. 



2516, 



VOL. 



100] 



charge through a short drowned pipe. The apparatus; 

 is described, and the coefficients of discharge for a six- 

 inch short pipe without mouthpieces at either end, and 

 with the inlet projecting and not projecting inwards 

 respectively, as well as for different combinations of 

 mouthpieces at inlet and outlet, are given. A biblio- 

 graphy of the subject is attached to the paper. 



ASTRONOMICAL CONSEQUENCES OF THE 



ELECTRICAL THEORY OF MATTER.^ 

 /^ERTAIN complications have recently been intro- 

 ^ duced into theoretical physics or physical philo- 

 sophy which, though not of immediate application to 

 engineering, should have an interest for all educated 

 people. 



Ihe doctrine of relativity is based essentially on two 

 negative experiments. One of these was conducted by 

 me at Liverpool, and is fully recorded in the Philo- 

 sophical Transactions of the Royal Society for 1893 and 

 1894. The outcome of the experiment is to show that 

 the velocity of light is not affected in the neighbour- 

 hood of rapidly moving matter; thus, in language 

 appropriate to aether, implying that the aether is sta- 

 tionary in space and cannot be carried along by moving 

 matter; that there is no viscous or frictional drag 

 between matter and aether. The other and more 

 famous experiment is that of Michelson and Morley, 

 which proves that the time of a light-journey to and. 

 fro between points fixed to the earth is not affected by 

 azimuth ; which therefore appears to imply that the 

 earth is not moving freely through the aether, as the 

 first experiment requires, but that the adjacent aether is 

 stagnant with respect to the earth's surface, as if a 

 layer of some thickness were fully carried along with 

 the earth in its motion through space. 



(I must here say that this is a conclusion which, 

 if admitted, would involve many difficulties, and would 

 complicate the relation between aether and niatter 

 amazingly.) 



The two experiments are thus contradictory, sug- 

 gesting that the wording of the conclusion in terms 

 of aether may be wrong; and inasmuch as all experi- 

 ments on the aether have so far given negative results 

 except when there was some movement of matter rela- 

 tive to matter, a doctrine of relativity has arisen which 

 begins by postulating that such experiments always 

 will give negative results, that the properties of an 

 aether can never be ascertained, that things go on as 

 if space were empty, that movement of matter has no 

 meaning except with reference to other matter, and 

 hence that in all probability the aether does not exist. 

 I ought perhaps to make it clear that I myself do not 

 hold this doctrine; but on that subject I have expressed 

 my own position in my British .Association address, 

 published by Messrs. Dent and Sons under the title 

 " Continuity." 



How the velocity of light, which is an undeniable 

 and metrical fact, can thus be understood or sys- 

 tematised, without a medium possessed of definite 

 physical properties, seems to conservative physicists a 

 substantial difficulty at the outset. Nevertheless, they 

 are willing to admit that questions directly addressed 

 to the aether have always received negative replies : 

 always except once — the measurement of the finite and 

 definite velocity of light, both in free space and in 

 transparent matter. Beyond this, the three saJient 

 ootical phenomena — viz. the Bradley aberration, the 

 Fizeau convection, and the Doppler change of fre- 

 quency — all involve motion of matter relative to matter. 



' Abridgment of a lecture delivered to the student-members ofthe Instttu- 

 lio" of Electrical Engineers on November 23, 1917, by Sir Oliver Lodge, 

 F.R.S. 



