Jan. 29, 1874J 



NA TURE 



253 



of the atmosphere as to enable it to quench, in so short a 

 distance, so vast a body of sound ? As I stood upon the deck 

 of the Irene, pondering this question, I became conscious 

 of the exceeding power of the sun beating against my back and 

 lieating the objects near me. Beams of equal power were falling 

 on the sea, and must have produced copious evaporation. That 

 the vapour generated should so rise and mingle with the air as to 

 form an absolutely homogeneous mixture, I considered in the 

 highest degree improbable. It would be sure, I thought, to 

 streak and mottle the atmosphere with spaces, in which the air 

 would be in different degrees saturated, or it might be displaced, 

 by the vapour. At the limiting surfaces of these spaces, though 

 invisible, we should have the conditions necessary to the produc- 

 tion of partial echoes, and the consequent waste of sound. 



Curiously enough, the conditions necessary for the testing of 

 this explanation immediately set in. At 3.15 r.M. a cloud threw 

 itself athwart the sun, and shaded the entire space between us 

 and the South Foreland. The production of vapour was checked 

 by the interposition of this screen, that already in the air being 

 at the same time allowed to mix with it more perfectly ; hence 

 the probability of improved transmission. To test this inference 

 the steamer was turned and urged back to our last position of 

 inaudibility. The sounds, as I expected, were distinctly though 

 faintly heard. This was at 3 miles' distance. At 3} miles 

 we had the guns fired, both point blank and elevated. The 

 faintest thud was all that we heard, but we did hear a thud, 

 wliereas we had previously heard nothing, either here or three- 

 quarters of a mile nearer. We steamed out to 4I miles, when 

 the sounds were for a moment faintly heard, but they tell away 

 as we waited ; and though the greatest quietness reigned on 

 board, and though the sea was without a ripple, we could hear 

 nothing. We could plainly see the steam-puffs which announced 

 the beginning and the end of a series of trumpet-blasts, but the 

 blasts themselves were quite inaudible. 



It was now 4 P.M., and my intention at first was to halt at 

 this distance, which was beyond the sound range, but not far 

 beyond it, and see whether the lowering of tlie sun would not 

 restore tlie power of the atmosphere to transmit the sound. But 

 after waiting a little, the anchoring of a boat was suggested ; 

 and though loth to lose the anticipated revival of the sounds 

 myself, I agreed to this arrangement. Two men were placed in 

 tlie boat, and requested to give all attention so as to hear the 

 sound if possible. With perfect stillness around them, they heard 

 nothing. They were then instructed to hoist a signal if they 

 should hear the sounds, and to keep it hoisted as long as the 

 sounds continued. 



At 4.45 we quitted them and steamed tow.ardsthe South Sand 

 Head lightship. Precisely fifteen minutes after we had separated 

 from them the flag was hoisted. The sound, as anticipated, 

 had at length succeeded in piercing the body of air between the 

 boat and the shore. 



On returning to our anchored boat we learned that when the 

 flag was hoisted the horn sounds were heard, that they were suc- 

 ceeded after a little time by the whistle sounds, and that both 

 increased in intensity as the evening advanced. On our arrival 

 of course we heard the sounds ourselves. 



The conjectured explanation of the stoppage of the sounds 

 appeared to be thus reduced to demonstration, but we pushed 

 the proof still further by steaming farther out. At 5f miles we 

 halted and heard the sounds. At 6 miles we heard them dis- 

 tinctly, but so feebly that we thought we had reached the limit 

 of the sound range. But while we waited the sound rose in 

 power. We steamfd to the Varne buoy, which is 7-J miles from 

 the signal station, and heard the sounds there better than at 6 

 miles distance. 



Steaming on to the Varne lightship, which is situated at the 

 other end of the Varne shoal, we hailed the master, and were 

 informed by him that up to 5 I'.M. nothing had been heard. At 

 that hour the sounds began to be audible. lie described one of 

 them as " very gross, resembling the bellowing of a bull," which 

 very accurately characterises the sound of the large American 

 steam whistle. .\t the Varne lightship, therefore, the sounds 

 had been heard towards the close of the day, though it is 125 

 miles from the signal station. 



What is the full meaning of this result? Imagine a man in 

 an anchored biiat at 2 r.M. at a distance of 2 miles from the 

 Foreland, and suppose him possessed of instruments which would 

 enable him to measure the growing intensity of the sound. Ap- 

 plying the law of inverse squares, to carry the sound to six times 

 the di;tance, its intensity at 2 miles would have to be augmented 



36 times. But the Varne lightship is more than 6 times 2 miles 

 from the Foreland. Supposing no absorption or partial reflection 

 to occur, the observer would have found that by the lowering of 

 the sun the sound at his position had at 6 P.M. risen to more than 

 forty-fold the intensity which it possessed at 2 P.M. In reality 

 the augmentation was still greater. 



( To be continued^ 



BIRMINGHAM NATURAL HISTORY AND 

 MICROSCOPICAL SOCIETY 



At the annual soiree, held on Tuesday, December 16, 1873, 

 celebrating the sixteenth year of the existence of the society, 

 Mr. W. R. Hughes, F.L.S., the president, gave, at the request 

 of the committee, an address on "' The recent Marine Excursion 

 made by the Society to Teignmouth." After alluding to the apt 

 and graceful remarks of his predecessor in office (Rev. H. W. 

 Crosskey, F.G..S,) twelve months ago, on the advantages of the 

 study of Natural History, and then describing the preliminary 

 arrangements in connection with the excursion which have already 

 been detailed in Nature, vol. viii. pp. 334;aiid 469, Mr. Hughes 

 stated that upwards of 20 members of the society, including 

 several ladies, proceeded from Birmingham and assembled at the 

 headquarters at Teignmouth on Monday, September i, on which 

 day the dredging operations commenced on board the yacht A'udy 

 with satisfactory results. These were carried on during the 

 week, and have already been described in Nature ; the 

 principal feature being the capture of the pedunculate form of 

 Anteiion rosaceus (Comaliila rosaeea), the rosy feather star, in- 

 cluding representatives of 1 2 genera of Echmodermata and about 

 40 species of llydrozoa and Polyzoa, the last of which had been 

 mounted and presented to the society by his friend aud colleague, 

 Mr. A. W. Wills, to whom the Society were also indebted for life- 

 like drawings of the Antedon in various stages of development. 



Mr. Hughes then proceeded to speak of the moral of the 

 marine excursion. So far as he was informed it was the first 

 of its kind that had been undertaken by any society carrying on 

 its operations in an inland district like Birmingham, far removed 

 from the sea, and that point was in itself noteworthy, and might 

 contribute to raise the status of the society and cause its example to 

 be followed by others of a kindred nature. He thought it was 

 pretty well agreed among the members that the excursion was 

 attempted properly, and on the whole carried out successfully. 

 The members who took part in it had been stimulated and en- 

 couraged in their project by the hearty and unanimous way in 

 which it was adopted by others whose studies lay in diffe- 

 rent directions, by praise from Nature, that most cultivated of 

 scientific serials, and by "good words "from the local press. 

 The results might not have satisfied all. Ciicumstances rendered 

 the absence of many old supporters of the society unavoidable. 

 It was planned a little too late in the season, and many of the 

 microscopic animals they dredged had played their part in the 

 great problem of life, and empty cells alone remained where many 

 a delicate .and beautiful organism had spread its feathery plumes 

 "in the dark unfathomed caves of ocean." Too much time was 

 devoted to the dredging, and not sutlicient for subsequent inves- 

 tigation of the proceeds. Still the members had enjoyed the 

 rare opportunity of examining many beautiful marine animals 

 under the microscope which they could not have hoped for at 

 home. And the excursion had done much to promote exchange 

 of thought and friendliness among those taking part in it. 

 Doubtless if a similar one were planned in 1874 the members 

 would profit by the experience of the late one, and Mr. Hughes 

 commended such to the consideration of the committee, and sug- 

 gested that the members should make it the subject of their 

 annual holiday, especially as ladies were now for the first time 

 admissible as members. The President stated he could not close 

 his remarks to an assembly composed of naturalists and those 

 who had evinced a taste in their pursuits, without alluding to the 

 fact that must have impressed most of them, viz. : that the study 

 of marine zoology had in these days attained an interest second 

 to that of no other branch of natural history, and that the exist- 

 ence and habits of the denizens of " the great and wide sea" 

 were discussed as familiarly in the newspapers of the day as the 

 events of social and political life. As further evideiice, Mr. 

 Hughes alluded to the record, almost surpassing any story in 

 the " Thousmd and One Nights " contained in that most charming 

 of books "The Depths of ilie .Sea," of the researches in t:eep- 

 sea dredging, by Prof. Wyville Thomson, F.R.S., and Dr. 



