128 



NATURE 



[December 7, 1899 



The direction from which they are- heard is constant, and 

 that is the south or south east. I have heard them west of me 

 when down in the extreme south of the district, but never north 

 of me. On the other hand, I have been told by captains of 

 river-going steamers that they have heard these reports to their 

 north. These gentlemen, however, ply along waters outside 

 the range of my observations, which lie on the mainland and 

 its adjacent waters. 



These Guns are always heard in triplets, i.e. three guns are 

 always heard, one after the other, at regular intervals, and 

 though several guns may be heard the number is always three 

 or a multiple of three. Then the interval between the three is 

 always constant, i.e. the interval between the first and the 

 second is the same as the interval between the second and the 

 third, and this interval is usually three seconds, though I have 

 timed it up to ten seconds. The interval, however, between the 

 triplets varies, and varies largely, from a few seconds up to 

 hours and days. Sometimes only one series of triplets is heard 

 in a day ; at others, the triplets follow with great regularity, 

 and I have counted as many as forty-five of them, one after the 

 other, without a pause. 



The report is exactly like the firing of big guns heard from 

 a distance with this peculiar difference, that the report is 

 always double, i.e. the report has (as it were) an echo. This 

 echo is so immediate that I can best describe its interval by an 

 illustration. Suppose a person standing near the Eden 

 Gardens heard the 9 o'clock gun fired froni Fort William, he 

 would first hear the report of the gun and its immediate echo 

 from the walls of the High Court. The Barisal Guns sound 

 exactly like this, only as if heard from a distance of several 

 miles, very much the same as the sound of the Fort gun heard 

 at Barrackpore on a clear night in the cold weather. 



The report varies little in intensity, and I cannot recollect 

 that there was much difference in the sound, whether heard at 

 Barisal itself or some 70 or 80 miles to the south at the extreme 

 end of the district. The state of the atmosphere may affect it, 

 but to no appreciable extent. 



The Backergonian peasant is celebrated for the bombs he is 

 in the habit of firing at his weddings and festivals, and many 

 residents have asserted they can distinguish no difference between 

 the reports of these festive bombs and the so-called "guns" ; 

 but to any one with a fairly acute sense of hearing, who listens 

 attentively, the difference is very marked, and their assertions 

 are completely refuted by the facts — 



(i) that wedding bombs vary very noticeably in the intensity 

 of their sound ; 



(2) are wanting in the very marked feature of the triplets, and 



(3) are naturally confined to the wedding season, a very 

 short season in each year, whilst the Birisal Guns are heard 

 almost throughout the year, and very noticeably during the 

 annual fast — the Roza — when, of course, there can be no 

 festivals of any kind. 



Letter from Geological Surveyor-General, Bengal. 

 I HAVE to thank you for your most interesting report on the 

 Barisal Guns. What you say about following the sounds in a 

 launch is very interesting, and points to a Seismic origin, that is 

 to say, that wherever the sounds came from they really origin- 

 ated locally, wherever you were at the time. In this case, 

 following them would be like trying to reach the foot of a 

 rainbow, whereas if they originated in surf on the sea-shore, or 

 the falling-in of river-banks, they should be traceable to their 

 source. R. D. Oldham. 



matter ; it may, too, be of interest in connection with the recent 

 letters which have appeared dealing with the capture of butter- 

 flies by birds. 



Continental butterflies appear to be remarkably tame. I was 

 constantly able to catch Podaliarius and other kinds with the 

 hand. D. Wilson-Barker. 



Greenhithe, November 27. 



Butterfly Shadows. 



While photographing insects lately in the hills above Pegli 

 (Italy), I was much struck by the curious way in which many of 

 the butterflies turned and shifted their position after they 

 had settled, their apparently eccentric behaviour making it 

 difficult to obtain a good picture. It suddenly struck me that 

 this turning and shifting was the result of an endeavour to settle 

 in such a position as would cast no shadow, thereby ensuring 

 to themselves less risk of detection. This seemed to be a 

 motive particularly with such butterflies as Circe, Semele and 

 Janira ; and its success as a method of concealment was very 

 striking in the case of Circe, which constantly settles on the bark 

 of trees or on the rocky ground. 



I submit this observation with the hope that it may attract 

 the notice of others who are able to give more attention to the 



NO. 1 571, VOL. 61] 



A Canadian Lake of Subterranean Inflow. 



Imagine a cliff about 180 feet in height, rising almost per- 

 pendicularly from the steamboat landing at Glenora on the south 

 side of the Bay of (^uinte, a great arm of Lake Ontario, and 

 perched immediately on the top of the cliff, within 300 feet from 

 the edge, a lake of clear fresh water about one a half miles long, 

 with a width of about three-quarters of a mile, its waters con- 

 tinually flowing out to give the power which operates the 

 Glenora mills, but its inflow invisible, and yet steadily main- 

 tained from month to month and from year to year. This is 

 the Lake-on-the-Mountain. 



Various origins have been suggested in accounting for the 

 inflow. That its source is not attributable to springs from any 

 possibly higher grounds in the same county seems established 

 by the fact that during the long drought in the months of August 

 and September of this year the level of the lake was well main- 

 tained. The source is, I think, rather to be sought in the 

 Trenton limestone area twenty-five or thirty miles to the north- 

 eastward of the Bay of Quinte. The dip of the rocks is favour- 

 able, and for the whole distance and into the Laurentian area 

 beyond there is a .steady rise until at about fifty miles away a 

 height of nearly 400 feet above Lake Ontario is reached. A 

 fair amount of rain fell in this higher country during the drought 

 elsewhere. 



To ascertain their bearing on the origin of the inflow, I this 

 past summer took a series of depths and temperatures in the 

 lake. Whilst a considerable part of its area was shallow, not 

 exceeding a few feet, the lake was found to have, close along- 

 side its southern boundary, a great rent, as it were, in its 

 bottom, of towards a mile long, one-third of a mile or more 

 wide, and varying from 7Sto 100 feet deep. That this rent is 

 due to a widened fault in the Trenton limestone here is very 

 probable, and the same forces which gave rise to this fault may 

 also account for a subterranean connection with higher ground 

 many miles away. The temperature readings were equally 

 interesting. In Lake Ontario, at its outlet opposite Kingston, 

 during August, the surface of the water ranged in temperature 

 around 72° F., and at a depth of 78 feet (the bottom) it was 

 56^° F., which latter was very much colder than during last 

 and some previous years. At the Lake-on-the-Mountain, whilst 

 the temperature of the surface was 74!° F., at 30 feet depth 

 it was 694° F., at 45 feet 47° F., at 60 feet 43° F., and at 

 99 feet 42° F. Thus, whilst during the first thirty feet there 

 was not very much change in the temperature, between thirty 

 feet and fo>ty-five feet there was a rapid fall of twenty-two and 

 a half degrees, and between the latter depth and the bottom at 

 ninety-nine feet a further fall of only five degrees. 



Andrew T. Drummond. 



Cause of Recent Sunset Colours. 



May I suggest to your readers that the striking colours of 

 the recent sunsets are possibly due to the dust in the air from 

 the Leonid meteors? 



They certainly remind one of the sunsets after the Krak- 



atoa eruption. 



Horace Darwin. 



The O'rchard, Huntingdon-road, Cambridge, 

 December 4. 



Substitute for Gas in Laboratories. 



It is proposed to extend the modern side of a large secon 

 dary school by the erection of chemical and physical labo- 

 ratories and lecture-rooms. The school, however, is some 

 miles distant from any town which has a gas supply, so that 

 it is necessary to consider what is the best substitute. I am 

 interested in the arrangements, and shall be thankful if any of 

 your readers will give me their experience on this point. It is 

 proposed that the laboratories will accommodate forty boys 

 working at one time. William Gannon. 



County Technical School, Stafford, December 4. 



