March 3, 1882.] 



KNCWI.EDGE 



375 



soon weakened, and it is not unusual in stormy ■weather to 

 put on additional battery power to compensate for the loss. 



The electric conductivity of moist air has been a subject of 

 dispute ; some electricians liave held that humid air acts as 

 a conductor of electricity ; and others have maintaLaed that 

 it does not. Recent experiments of M. Marangoni support 

 the latter theory very decidedly, for he finds that a Leydcn 

 jar, heated so as to prevent condensation of moisture on 

 its glass walls, and thus arrest surface conduction, gives 

 a long spark as in the driest air. When, however, the 

 precaution of heating the walls of the jar is not taken, the 

 moisture condenses on the latter, and, forming a thin film 

 of water, causes a silent discharge, which might be mis- 

 taken for a slow discharge through the conducting air. It 

 follows from these experiments that the loss of electricity 

 on telegraph lines is wholly due to surface conduction over 

 the wet and dirty insulators, or leakage along entangled 

 threads and branches of trees, at particular points, and not 

 to a general discharge into the saturated air. 



Lightning, or atmospheric electricity, is occasionally 

 attracted to the wires, and passes along them, disturbing the 

 indications of the instruments. Telegraphists are always 

 exposed to danger during a thunderstorm. In the summer 

 of 1859, a youth employed in the telegraph department 

 of one of our principal railways was seriously injured 

 by the physiological effects of an electric shock, received 

 while he was sending a message on the double-needle 

 instrument. A storm was raging at the time, and the clerk 

 did not take the precaution to avoid touching the metallic 

 parts of the instrument. At that period, the many 

 ingenious contrivances for diverting the lightning now in use 

 had not been thouglit of. I ha\e known the fine silk-covered 

 wires used in certain parts of the needle telegraphs fused into 

 an amoi-phous mass. When the currents of atmospheric 

 electricity were not so intense, they usually demagnetised 

 the needles, causing them to deflect the reverse way. 



The Aurora Borealis or Northern Lights will some- 

 times cause a disturbance in telegraphic communica- 

 tion. The long lines and cables are more liable to be 

 affected by the Aurora. There was a disturbance of this 

 kind from Aug. 11 to 14, 1880. According to the report 

 of Privy Councillor Ludewig, of the Central Telegraph 

 Department, Berlin, it seems to have manifested itself 

 throughout the greater portion of the northern section of 

 the Eastern hemisphere, sending off, however, a southerly 

 stream in the direction of Mozambique, which reached to 

 Natal. It does not appear that the western continent 

 was affected. The general features of the disturbance 

 consisted of manifestations of the presence of strange 

 currents (earth currents as they are called) of fluctuating 

 intensity, the durations and fluctuations varying in 

 different localities, and the direction of the currents 

 changing frequently. This last feature would seem to 

 indicate a movement of revolution, or at least of approach 

 and recess, with regard to some line or point. These dis- 

 turbances were traceable alike in underground lines and 

 in lines carried through the open air. In Germany all the 

 longer lines were very much disturbed, in the ways men- 

 tioned, on Aug. 1 2, from noon till late at night The inter- 

 ruptions frequently involved the omission of several 

 signs, or even words, and in the Morse apparatus, 

 continuous strokes appeared on the paper. 



There are other causes of disturbance to which 

 telegraph lines are liable. Kite-tails entangled in the 

 ■wires will, if a shower of rain comes on, cause con- 

 tact : the electricity will flow from one wire to the 

 other, so that a message, say, from London to Birmingham, 

 may pass through three or four different circuits, and give 

 rise to provoking confusion and delay. I have seen the 



dead body of a large bird lying across the wires of a railway 

 telegraph line. 



Aproj/oa of the feathered tribe, some interesting 

 facts were recently brought out in a paper by M. C. 

 Nielsen, of Christiania, on the impression produced 

 upon animals by the resonance of the vibration of tele- 

 graph wires. It is found that the black - and - green 

 woodpeckers, for example, which hunt for insects in the 

 bark and in the heart of decaying trees, often peck 

 inside the circular hole made transversely through tele- 

 graph posts, generally near the top. The phenomenon is 

 attribxited to the resonance produced in the post by 

 the vibration of the wire, which the bird mistakes als 

 the results of the operations of worms and insects 

 in the interior of the post. Everyone knows the 

 fondness of bears for honey. It has been noticed that 

 in mountainous districts they seem to mistake the 

 vibratory sound of the telegraph wires for the grateful 

 humming of bees, and, rushing to the posts, look about 

 for the hive-s. Not finding it on the post, they scatter the 

 stones at its base, which help to support it, and, dis- 

 appointed in their search, give the post a parting pat 

 with their paw, thus showing their det<'rmiiiation, at 

 least, to kill any bees that may be about. Indisputable 

 traces of bears about prostrate posts and scattered stones 

 prove that this really happens. With regard to wolves, 

 again, M. Nielsen states that when a vote was asked 

 for the first great telegraph lines, a member of the 

 Storthing said that, although his district had no direct 

 interest in the line proposed, he would give his vote in 

 its favour, because he knew the lines would drive the 

 wolves from the districts through which they passed. It 

 is well known that to keep off the ravages of hungry 

 wolves, in winter, the farmers of Norway set up poles con- 

 nected together liy a line or rope, under which the wolves 

 would not dare to pass. " And it is a fact," M. Nielsen 

 states, "that when, twenty or more years ago, telegrajih lines 

 ■were carried over the mountains and along the valleys, the 

 wolves totally disappeared, and a specimen is now a rarity." 



Water-careyi.ng Tobtoises. — At a recent meeting of the San 

 Francisco Academy of Sciences a tine specimen of the desert lanil 

 tortoise, captured at Cajon Pass, San Bernardino County, was 

 sliown, and Professor E. T. Cox related some curious circumstances 

 in connection with it. This tortoise, wliich is aslarge as a good-sized 

 bucket, is a native of the arid regions of Caiifornia and Arizona. 

 On one being dissected, it was found that it carried on each eido a 

 membrane, attaclied to the inner portiijn of tiie sliell, in wliich was 

 about a pint of clear water, the whole amount being about a quart. 

 Professor Cox was of opinion that the water was derived from the 

 secretions of the giant barrel cactus, on which the tortoise feeds. 

 This cactus contains a great deal of water. The tortoise is found 

 in sections of the country where there is no water, and -where there 

 is no vegetation but the cactus. A traveller siifi'i'ring from thirst 

 could, in an emergency, supply himself with water by killing a 

 tortoise. They are highly prized by Jlexicams, who make from 

 thera a delicious soup. They are oftentimes attacked by foes, 

 both for their water and also for their flesh. They arc overcome 

 by the foxes, and killed by being dragged for miles over the country 

 at a pretty rapid pace. Mr. Bedding afterwards stated that he was 

 on the Gallapagos Islands in 18i9, wlien he assisted in capturing 

 92 land tortoises, varying in weight from 450 lb. to 6001b. each. 

 These they brought to San Francisco, where they sold them for 

 more money than the whole of the ship's cargo of lumber made. 

 They were two months on board, yet they neither ato nor drank 

 anything, though food and water were offered them. When killed, 

 however, considerable quantities of water were found in each of 

 them. They lived on the high lava rocks of the islands, where there 

 are no springs or streams, and the only dependence of animal life 

 for water is necessarily upon the irregular and uncertain rain 

 showers. These were of a different species from the one shown. 

 It was generally admitted that it would be useful if the habits and 

 peculiarities of these animals could be noted, and some trustworthy 

 information as to how they collect and secrete their water obtained. 



