HARD WICKE' S S CIENCE- G O SSI P. 



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having great powers of vision, and the means of 

 taking in a very large field of view, simply see the 

 sunward land on the other side, and fly towards it. 

 The difficulty here is merely a question of degree, 

 whether or not some of the channels actually crossed 

 are too wide for this. In " Nature," November 3rd, 

 of last year, is a letter from Mr. Warde Fowler, 

 describing the migration of swallows on the south 

 coast of England. This shows that they take long 

 journeys from west to east in search of a narrowing 

 part of the channel. 



An officer of the German Navy, Captain Sebelier, 

 has recorded some facts that lessen this difficulty. The 

 islanders of the Marshall group in the North Pacific 

 Ocean make long voyages in their canoes towards 

 islets that are far beyond their vision-reach, and do 

 this without any astronomical aid. From twenty to 

 fifty canoes start together and keep within signal- 

 reach of each other, and thus a large extent of sea is 

 under survey. They advance until the islet is sighted 

 by one or the other of the canoes. When such is the 

 case, that one takes the lead, and the rest follow in 

 accordance with the signal. 



That birds do signal each other is well established. 

 May not the migrating birds guide each other on this 

 principle ? The Marshall islanders rest at nightfall, 

 but the birds fly so rapidly that daylight is long 

 enough to serve them fully in covering the widest of 

 their transmarine journeys. Nevertheless they some- 

 times perish. I witnessed an example of this on the 

 coast of Greece, near Cape Matapan. Had sailed 

 from Malta in a small schooner in the spring, and 

 encountered a severe gale. A number of swallows 

 and martins settled in the rigging after the gale, and 

 were so exhausted that they made no attempt to 

 escape when we took them in our hands. They all 

 died in spite of our attempts to aid their recovery. 

 They appear to have been blown from their course 

 by the gale. 



Caprices of Lightning. — We are told that an 

 electric discharge follows the line of least resistance, 

 and lightning conductors are placed accordingly to 

 entice the discharge to follow an easy and harmless 

 route. It does so usually, but not always. In the 

 "Bulletin de la Societe Vaudoise des Sciences 

 Naturelles " (No. 95), M. H. Dufour narrates some 

 remarkable exceptions. A storm coming from the 

 West passed over some gasworks and tall poplars 

 without any discharge, but wrecked a house lying 

 just below them on the leeward side. Again, at 

 Penthalaz, the spire of a church was spared, while a 

 house near to it was struck. It may be that in these 

 and similar cases the cause of the discharge was 

 nearer to the horizontal than to the vertical, not 

 from a cloud to the earth, or vice versd, but between 

 two beds of air or vapour lying at nearly the same 

 elevation. We may frequently see discharges taking 

 place between two clouds that are both at nearly the 



same elevation, and it is therefore not improbable 

 that similar differences of potential may exist between 

 columns of air near the ground at times of violent 

 atmospheric disturbances. 



The Raising of Egyptian Monoliths.— As 

 some of these reach a height of one hundred feet, and 

 weigh some hundreds of tons, the question of how 

 they were raised opens many speculations. One of 

 the most recent of these is by M. Arnaudeau, who 

 suggests that the obelisk being placed horizontally 

 with its base towards the pedestal, a circular water- 

 tight enclosure was raised equal in height to the 

 obelisk. Then blocks of wood or other floats were 

 fixed to the upper part of the obelisk and water was 

 let into the enclosure, whereupon the monolith rose 

 gradually to the upright position, and, being partly 

 sustained by the water, was easily handled for 

 adjustment on its intended base. 



This reminds me of a contrivance attached to Lord 

 Rosse's great telescope at Parsonstown, with which I 

 was not acquainted until I saw it in operation, and 

 which may be equally new to most of my readers. 

 The speculum at the object end is of course very 

 massive, and demands a counterpoise. This is 

 obtained by hanging heavy weights from the eye end. 

 But the leverage at which these weights act neces- 

 sarily varies according to the inclination of the tele- 

 scope. When it is pointed nearly to the vertical this 

 leverage is very short, and it increases as the great 

 tube turns towards the horizontal. Therefore, in 

 this case, the counterpoising weight requires gradual 

 diminution. This is obtained by the aid of a deep 

 water-trough, into which the counterpoise weights 

 gradually dip as the eye end of the telescope descends, 

 and thus their weight is first partially sustained by 

 the water as they dip into it, and then fully sustained 

 when they rest on the bottom. One weight succeeds 

 another thus, and by skilful adjustment of this gradual 

 lightening, the balance of the great tube is maintained 

 at all inclinations. 



Freezing Water-pipes. — "Nature" tells us 

 that the architect who designed the new Medical 

 School in Paris took so little pains about the distri- 

 bution of the water-pipes that in . very cold weather 

 the laboratories for physiology, bacteriology, experi- 

 mental pathology, &c, are wholly deprived of water. 

 It is by no means necessary to cross the Channel to 

 find examples of similar ignorance of the elementary 

 principles of science among architects and builders. 

 Now that there are so many empty houses in and 

 around London and other great towns, and the 

 competition for tenants is consequently very keen, 

 the remedy is in the hands of intending tenants. If 

 they firmly refuse to occupy any house the water-pipes 

 of which are imperfectly protected from exposure to 

 frost, and unprovided with the means of emptying 

 them when frost is threatened, a change will soon 



