30 



NA TURE 



[December 12, 1895 



coloured Calanus on the beach with his hand, shows that these 

 creatures had passed through some unfavourable conditions. 

 Dr. Murray has endeavoured to show that these deep-sea 

 animals are brought to the surface through the movements of 

 large bodi«s of water during gales or during calms following 

 gales. However this may be, their proper habitat is certainly 

 at the bottom. When they do come to the surface they form 

 oily-like streaks or small spots, where herrings and other fish 

 and birds may be seen feeding upon them. The Nyctiphanes 

 at any rate remain but a very short time at the surface. On 

 one occasion in Kilbrennan Sound we were attracted to a spot 

 where guillemots, gulls, and other birds were feeding, and we 

 found that their stomachs were filled with perfectly fresh 

 Nyctiphanes, and the Nyctiphanes themselves could be distinctly 

 seen on the surface for a short time. The fishermen shot a 

 circle trawl-net around this spot, and procured twelve boxes of 

 herrings, the stomachs of which were distended with these 

 Crustaceans in all stages of decomposition. I can show these 

 stomachs to any one visiting this Station. 



In my previous letter I mentioned that we had captured 

 herrings in the deep water with their stomachs filled with these 

 Crustaceans, and skate, which feed at the bottom, have been 

 taken in depths over 50 fathoms with herrings in their stomachs. 

 When the herrings' stomachs are filled with adult Nyctiphanes, 

 as above stated, the herrings are not commonly called "gut- 

 poke," or at least are not looked upon as diseased. The so- 

 called disease is attributed to those herrings which have been 

 feeding chiefly upon the young Nyctiphanes, or "black-eye." 



I do not claim that there is anything new on this subject in 

 my letters, nor do I see anything new in that of Mr. Calderwood, 

 except the statement that Copepods alone are the cause of the 

 the so-called "gut-poke" disease, which I do not believe. 

 The whole of this information was published many years ago. 

 In a lecture delivered in November 1887, as reported in the 

 Scotsman of Noveinber 2^, Dr. Murray said regarding- the 

 " poke-gut " : — 



" There was also a kind of herring called the ' poke-gut ' 

 herring, which was supposed to be suffering from some disease 

 or complaint. This was a herring whose stomach was distended 

 with food, which consisted of one or other of the minute animals 

 to which he had referred. One of the commonest things to be 

 told on the west coast was that the ' poke-gut ' herrings were 

 riot fit for food, and would not cure. The fishermen told them 

 that they had eaten some ' black stuff,' the effect of which was 

 to make them sick, that it burned a hole in their bodies, and 

 acts as if they had eaten quicklime. For a long time he was 

 very doubtful as to what the explanation of this belief could be, 

 but he ultimately found that the cause of it was this — that the 

 poke-gut herrings had been feeding on the young Nyctiphanes. 

 The eyes of these creatures are very black indeed (as Dr. Murray 

 showed by exhibiting a bottleful of the creatures in a preparation 

 of glycerine), and an accumulation of these in the stomach of the 

 herring gave the whole contents a very black aspect. On being 

 taken into the boat, decomposition set in very rapidly, the lining of 

 the stomach was speedily eaten away, and before long an actual 

 hole, as the fishermen said, was made in the body, out of which 

 this black mass exuded. In this 'poke-gut' state the herring, 

 however, was simply engaged in laying up a store of fat, the 

 nutritive processes of the animal laeing then exceedingly active. 

 When it had laid in this store of fat, the herring then sought 

 the shallow waters of the shore for the purpose of depositing its 

 spawn. Mr. Hoyle spent several months at Peterhead examin- 

 ing the stomachs of the herring to ascertain what they fed upon 

 during the fishing season, but the result of his investigations was 

 that he did not find in any one of them a full meal. Similar 

 results were obtained by Mr. Beddard at Eyemouth, and by 

 Prof. Herdman on the coast of Arran." 



Our observations on board the Medusa went to show that the 

 " poke-gut " condition of the herring was chiefly due to the large 

 number of young Nyctiphanes contained in the herrings' stomachs, 

 but Mr. Calderwood makes no mention of any Crustacea beyond 

 Copepods. Alexander Turbyne. 



Scottish Marine Station, Millport, Cumbrae, November 29. 



The Theory of Magnetic Action upon Light. 



I HAVE already pointed out that the various questions relating 

 to the theory of the action of magnetism upon light cannot be 

 disposed of by arguments based upon vague and obscure general 

 reasoning, but require a careful mathematical investigation for 



NO. 1363, VOL. 53J 



their elucidation. I therefore propose in the present letter to state, 

 as briefly as possible, the results to which an examination of Mr. 

 Larmor's theory leads, and to show how my own theory may be 

 amended so as to remove the objection concerning the discon- 

 tinuity of the E.M.F at an interface. 



I find that Mr. Larmor's theory requires that all the equations 

 of Maxwell's general theory of the electro-magnetic field should 

 remain unaltered, except the equation 



P z= - F - di/ldx, 

 which must be modified by the insertion of the additional terms 



-Pzi+ Pi''' + zd<p/dy - ydfdz (i) 



where/], /o,/:} are constants depending on the magnetic field, 

 and <p is a potential function. 



The first two terms are equivalent to introducing Hall's 

 effect ; but for the last two there is no justification whatever. 

 They are not required in optics nor in electro-magnetism. These 

 results, combined with Larmor's boundary conditions, prove my 

 statement that his theory makes the tangential component of 

 the E.M.F. discontinuous at an interface. 



In the next place, a satisfactory theory may be constructed by 

 modifying Maxwell's relation between E.M.F. and electric dis- 

 placement, keeping all the other equations unaltered. The pro- 

 posed modification is 



T=4ir//K+P,£-P,i .(2) 



It will be found that this hypothesis leads to exactly the same 

 equations of motion and boundary conditions as those given in 

 my paper in the Phi/. Trans., 1891 ; but that, in con.sequence of 

 the relation (2), the tangential component of the E.M.F. is con- 

 tinuous at an interface. The other boundary condition is, con- 

 tinuity of the tangential component of the magnetic force. 



According to Maxwell's theory, the electrostatic energy is- 

 given by the expression 



and if we assume that this result holds good when P is given by 

 the modified form (2), it will be found that all the results can be- 

 deduced by means of the principle cMeast action. 



Under these circumstances, I think I may justly claim to have- 

 placed the theory of Kerr's experiments on as perfect a basis as- 

 is possible in the existing state of electrical science. 



A. B. Basset. 



Fledborough Hall, Holyport, Berks, November 29. ' 



The Barisal Gun. 



I have read with interest Dr. Darwin's communication, in' 

 Nature for October 31, on "The Barisal Guns and Mist 

 Pouffers," and his request that the readers of your journal 

 should give accounts of their own experiences in this matter. I 

 refer him to the Theosophistma.ga.zme, vol. ix. p. 705, and vol. xi. 

 p. 409, for two articles upon my personal observations at Barisal 

 village itself, in the Gangetic delta. All the various theories 

 until then propounded by men of science to account for the 

 phenomenon in question were severally reviewed and pronounced 

 inadequate. I had intended writing a third and final article, but 

 found it impracticable to throw any further light upon this most 

 interesting problem, and so abstained. Dr. Darwin is quite 

 wrong in supposing that the sound of the "Barisal Gun" is- 

 "dull and distant," and that "it does not resemble artillery." 

 However the like sounds may seem to the Ostend lighthouse- 

 keeper, they were .so sharp and loud that I thought the 

 '"evening gun" was being fired at a cantonment in the village, 

 and asked a friend standing by if that were so. I shall not 

 encroach on your space to go into details, since the back 

 volumes of the Theosophist may be consulted at the British 

 Museum, and Dr. Darwin will make such use of them as he 

 sees fit. H. S. Olcott. 



Adyar, Madras, November 20. 



Remarkable Sounds. 



In connection with Profs. McKenny Hughes and J. P. 

 O'Reilly's letters on the above subject, suggesting the collection 

 of data as to the distance the sound of blasting, &c. , has been 

 heard, it may be interesting to state that the blasting o])erations 

 in the Charnwood Forest quarries (probably Bardon Hill) can 

 be distinctly heard on the higher ground to the south-west of 

 Atherstone, a distance of about eighteen miles. From the in- 

 tensity of the sound, I have little doubt that under favourable 

 conditions it may be heard very much further. 



Geological Survey, Leicesfer. C. Fox-Strangways. 



