586 



NA TURE 



[April 24, 1902 



Swarm of Velella. 



The brief note from Alassio by iMr. Isaac Thompson on the 

 extent and density of a swarm of Velella off that coast this 

 month recalls to my mind seeing a similar scene on each 

 of two occasions when staying at that place in April. On each 

 occasion of the swarm there was, as I well remember, a strong 

 wind from the east ; on each the shore became so thickly strewn 

 with the organisms as to become unpleasantly odorous from 

 their decay. Cii. S. Shekrington. 



Felixstowe, April 19. 



Referring to your correspondent's letter on the swarms of 

 this little marine animal that strewed the shores of the Riviera 

 di Ponente early in April, I was at Alassio and remarked that 

 the wind had been easterly for some days before the advent of 

 the swarm. Alassio is situated on a sandy bay facing the east ; 

 on the western side of the bay, two miles away, lies a fishing 

 village called Laiguelia ; here the Velella were in far greater 

 numbers, thickly piled on the shore, thinning off gradually 

 towards Alassio, while beyond Alassio, at the extreme eastern 

 end of the bay, the Velella were comparatively thinly scattered 

 on the sand. The clear horny oval disc over the little colony 

 of polypes, with its diagonally-set, triangular sail, places Velella 

 at the mercy of the winds ; a shoreward wind blowing for 

 several days must end in the wreck of the little " Barca di San 

 Giovanni " (boat of St. John), as the Alassian fishermen call 

 it. I am told it is usually in early June that the swarms are 

 swept ashore, and then in immense numbers — far more than 

 strewed the bay this April. The prevailing wind in summer at 

 Alassio is easterly. Rose Haig Thomas. 



Hotel Palais d'Orsay, Paris, April 21. 



Habits of the Gar-fish and Mackerel. 



Beyond the fact that the bodies of other fish are occasionally 

 pierced by them, no evidence seems to exist concerning the 

 special function of narrow elongated jaws of the gar-fish (Belone 

 vulgaris, Fleming). These fish are usually captured in drift 

 nets along with mackerel, and there appears to be some vague 

 idea among fishermen that they either guard or guide the 

 mackerel shoals. In the cases on record where a mackerel or 

 other fish has been pierced by the gar-fish, the upper jaw of the 

 latter has usually been found broken off and remaining in the 

 wound. This fact is inconsistent with the supposition that the 

 normal function of the elongated beak is to be used as a spear, 

 and there is no evidence that the gar-fish feeds on the flesh of 

 large fishes. 



Examination of the beak itself shows that the end of it is 

 formed by the tip of the lower jaw, which is about half an inch 

 longer than the upper. This tip is not hard and sharp, but soft 

 and blunt ; the upper jaw is narrower, and ends in a harder and 

 sharper point. Thus the lower jaw is by no means adapted for 

 use as a piercing weapon. Recently I opened the stomach of 

 one of these fish landed at Newlyn, and found in it the partly 

 digested remains of a slender silvery fish, which at the time I 

 could not identify. The next day I opened a number of mackerel 

 and found in some of them copepods and amphipods, but in 

 nearly all remains of fish food, and in one, two specimens of the 

 smaller sandeel {Amniodytcs tohiattus) only slightly digested. I 

 was then able to satisfy myself that the fish on which the Belone 

 had been feeding was also the sandeel, and I was impressed 

 with the similarity in the structure of the jaws between the 

 Belone and its prey. It then occurred to me that the proper 

 function of the beak of the Belone was to penetrate the sand in 

 pursuit of sandeels. The latter fish burrow into sand by means 

 of the projecting lower jaw, and it is evident that the beak of 

 the Belone is as well adapted for probing the sand, finding and 

 seizing the sandeel, as is the beak of the woodcock for probing 

 soft ground in search of worms and burrowing insects. The 

 flexible tip of the fish's beak is doubtless a sensitive tactile 

 organ, while the narrow toothed upper jaw is eminently fitted for 

 seizing and holding the slippery and agile prey. 



It seems very probable that special adaptation for the imrsuit 

 of sandeels in the sand explains, not only the peculiar beak of 

 Belone, but also the elongation and structure of the whole body. 

 Narrowing and elongation of the body are related in fishes and 

 many other animals to creeping or burrowing habits. Probably, 

 not merely the beak, but the greater part of the body of Belone 

 also is thrust into the sand in pursuit of its prey, and this would 

 explain why the dorsal and ventral fins are placed far back, so 



NO. 1695, VOL. 65"! 



that the propelling apparatus remains in the water, and why the 

 abdominal region is nearly cylindrical, with a somewhat flattened 

 ventral surface, without dorsal or ventral ridges. 



The fact that the mackerel were also feeding on sandeels 

 further suggests a special reason for the association between 

 mackerel and garfish. It is true that many predaceous fish eat 

 sandeels when they can get them, but the jaws of the mackerel 

 are not specially fitted for dislodging sandeels from the sand. 

 In the early part of the year mackerel feed largely on copepods 

 and other pelagic animals, having long, close-set gill-rakers 

 through which they can strain the sea-water, like clupeoid fishes. 

 In summer and autumn mackerel feed chiefly on small fishes 

 which swim near the surface, such as the young of sprats, 

 herring, gadoids, &c. But it seems probable that mackerel ac- 

 company the gar-fish in order to feed on the sandeels which leave 

 the sand in their efforts to escape from their special enemy. 



I have not yet made any observations on the food or habits of 

 the saury-pike (Scombercso.x saiiriis), but it is probable that, as 

 in the case of Belone, injury to pilchards or other fishes by the 

 beak of this fish is rather accidental than intentional. Couch 

 and Matthias Dunn believed that the saury-pike was the enemy 

 of the pilchard, and that it attacked the latter. When a number 

 of both kinds of fish were enclosed in a seine, many of the 

 pilchards had their eyes or bodies pierced by the beaks of the 

 saury-pikes, but the latter are very active and violent in their 

 movements, and if they were rushing about among a dense 

 crowd of pilchards, the beaks could scarcely fail to pierce the 

 latter. J. T. CUNNINGHAM. 



Flint Implements at Chelsea. 



While planting in the garden of this house last Wednesday, 

 I turned up a small flint implement, an inch and a half long 

 and an inch wide in the widest part. It is so thin and trans- 

 parent, that it is possible to read large print through it. This is 

 the second I have found, the previous one being angular and 

 pointed. A, B. Marshall. 



Belle Vue House, 92 Cheyne Walk, S.W., April 18. 



The Misuse of Coal. 



Pkof. Perry, in his manifesto in Nature of March 20 (with 

 which, subject to a reservation in respect of the following 

 extract, I venture reapectfully to agree) says (p. 464) :— 



" For the heating of buildings Lord Kelvin pointed out long 

 ago that the very law of thermodynamics which makes a heat- 

 power engine inefiicient makes it possible to obtain from one 

 unit of energy the eftect of 50 or 100 units by direct heating. . . 

 Discover the energy engine and you multiply your power 

 to heat buildings from coal, seventy and seven times." 



May I ask if Prof Perry adheres to the foregoing statement, 

 and if so, ask him through you to kindly add some elucidation 

 of it? Subscriber. 



Derby, April 15. 



"Subscriber" may be referred to § 196 of my book on 

 " Steam," where I explain Lord Kelvin's suggestion and give 

 a numerical example. I assume no better utilisation of coal 

 than one gets from a gas engine using Dowson g.is and practical 

 conditions, and yet here are the two answers for one pound of 

 coal : — 



(i) By direct heating, all the heat of the coal being given to 

 the air (it is unusual to give nearly so much), the air gets 

 S300 units (Centigrade pound) of heat. 



(2) By using a gas engine and reversed heat engine, 37,620 

 units of heat are given to the air. This is only four and a half 

 times and not the seventy-and-seven of which I somewhat 

 rhetorically spoke. But with the perfect energy engine of the 

 future we may get nearly six limes what we get from the gas 

 engine now. Also I considered an atmosphere at 10° C, the 

 air to be heated to 20° C.-for the warming of a building. If the 

 rise of temperature is only 5 degrees we get twice the benefit. 



It looks at first sight like a creation of energy, but this is not 

 so. The reversed heat engine (some refrigerating machines 

 work on this principle) receives work energy 1422 (specified in 

 heat units) ; this work is converted into heat 1422. and the extra 

 heat 36,198 is merely transfetred from air at 10 C. to air at 

 20° C. 



What is disadvantageous in the heat engine becomes advan- 

 tageous in the reversed heat engine, whether il is used for heating 

 or refrigerating. J. P. 



