234 



NATURE 



[April 21, 192 1 



(6) Change of direction can be produced (just as 

 it can in a planing bird) by lateral tilt of the body. 



(7) Rise and fall are certainly possible (due to forcing 

 up of air by waves), but I have been unable to observe 

 any cant of the planes which produces this. 



(8) The fish can easily outstrip a vessel doing 

 17 knots. 



(9) The majority of fish turn into the wind when 

 launching themselves. On December 12, 1919, simul- 

 taneous observations were made by two observers for 

 periods of 1^ ijiinutes upon the windward and lee- 

 ward sides of the ship. Twice as many fish "flew" 

 to windward as to leeward. In some counts the 

 results were as high as eight to windward without a 

 single fish going to leeward. 



(10) They can remain in the air for at least half 

 a minute (I fancy I have seen much longer flights 

 when in the cable ships). On December 18, 19 19, the 

 following flights were timed : — 10 seconds (three 

 times), 15 seconds (four times), 25 seconds, with tail 



muscle being downwards and forwards, and not 

 downwards and backwards. 



(15) The structure of these muscles is altogether 

 unlike that familiar in muscles performing the short, 

 quick strokes of flight, but is entirely what would be 

 expected of muscles acting tonically' as spreaders of 

 planes. F. Wood-Jonks. 



Universitv of Adelaide. 



"Space" or "/Ether"? 



Prof. Eddington (N.atuke, April 14, p. 201) chal- 

 lenges those of us who have asserted that "relativity 

 does away with the aether " to defend our statement. 

 He himself provides our defence. He tells us that Ms 

 aether — the Eether that relativity does not do away with 

 — "has not . . . density, elasticity, or even velocity." 

 But our aether — the aether of pre-relativity days, which 

 relativity has done away with — has all those pro- 

 perties. In particular, it has the last. The nineteenth, 

 century aether simply was a system relative 

 to which light had the normal and invariable 

 velocity c ; so that the velocity of light rela- 

 tive to a system which had, relative to the 

 aether, the velocity v was c+i;. That state- 

 ment conveys the very meaning and essence 

 of the old aether ; deny it, and the Fizeau and 

 Michelson-Morley experiments lose all signi- 

 ficance. 



Prof. Eddington 's word "aether" has 

 neither the denotations nor the connotations 

 of the old word. His use of it will receive 

 the support of Humpty-Dumpty, but not of 

 those wno consider that accuracy of thought 

 is intimately dependent upon the constancy 

 of the meaning of the words used to express 

 it. Norman R. Campbell. 



rig.4 



ri$.6. 



Fig. I. — General lines upon which the fish is built. 



Fie. 2. — The pectoral tin was placed in the position of flight, and the specimen then 



hardened in formalin. The right fin is represented cut through near its base. 

 Fig. 3. — Dissection of the dorsal or posterior mu-.cle (tinted), showing the depression 



in the general longitudinal muscle mass of the body into which the fin fits when 



hauled up and back by its retractor muscle. The tinted muscles in Figs. 3 and 4 



are indicated by the lines A- 

 Fig. 4. — Dissection of the ventral on anterior muscle (tinted). Numerous tendons pass 



the fin-rays from small pale muscle. Evidently the muscle hauls the rays and 



spreads the wing like a fan. 

 Fig. 5. — The ventral muscle removed to show the depression in the gill base skeleton 



which it occupies. 

 Fig. 6 — Diagram to show direction of action of the two muscle masses. 



splashes (twice), 28 seconds (numerous tail splashes, 

 once), and 30 seconds (numerous tail splashes, 

 once). 



(11) The dorsally situated mouth and the enlarged 

 ventral fluke of the tail-fin tell clearly that the fish is 

 one designed to make rushes upwards through the 

 water in search of food. 



(12) Its "flight" is only an extension of the flight 

 of the garfish. These fish also launch themselves 

 into the air, and without any planing, but merely by 

 their impetus, travel for a sufficiently long and rapid 

 " flight " to carry them — like a hurled spear — right 

 through the sail of a boat. 



(i-^) Only two main muscle masses are attached to 

 the base of the pectoral fin. The posterior muscle 

 pulls the fin upwards and backwards and folds it into 

 the "slot" for its reception. The anterior muscle 

 pulls the fin downwards and forwards and spreads 

 it as a plane. 



(14) These muscles do not produce "flight " move- 

 ments of the fin, the stroke of the ventral (anterior) 

 NO. 2686, VOL. 107] 



I AM indebted to Prof. Eddington (Nature, 

 .\pril 14, p. 201) for pointing so decisively to 

 the full issues of my argument (Nature, 

 .\pril 7, p. 171). The position may be clinched 

 thus : — The relativists may take away pure 

 space as an objective entity, but in so doing 

 they are " aetherising " or materialising the 

 space of the physical universe. So the 

 physicists get back their "aether " with some- 

 thing more; and "space," a fundamental 

 fact of human experience which has been 

 such a metaphysical enigma right down the 

 ages, at least becomes intelligible as the sub- 

 stratum of matter. The identification of 

 aether and space provides a mechanism of the uni- 

 verse, and will enable us to picture physically what is 

 meant by such phrases as "world-lines" and "twists 

 in space." 



Prof. Eddington 's reason why the quality of beauty 

 is not included in physical science and my own are 

 metaphysically identical, and the two propositions, 

 very differently framed, confirm one another. 



April 16. L. C. VV. Bonacina. 



Meteors on the Moon. 



The reported failure of Prof. Goddard to obtain 

 pecuniary support for his project to discharge a giant 

 rocket at the moon leads me to ask a question which 

 astronomers may answer. Why is it that no observer 

 has ever reported the descent of a meteor upon the 

 surface of our satellite? It seems reasonable to sup- 

 pose that meteoric falls must occur there as upon the 

 surface of the earth. According to the accepted esti- 

 mate, the earth receives about 20,000,000 meteorites 

 per diem. If that holds good, mutatis mutandis for 



