32 



SCIENTIFIC NEWS. 



[Jan. 13, iS 



New Use for Salt. — According to the American 

 Architect, the addition of salt to cement mortar in cold 

 weather preserves it from the bad effects of freezing. 

 The reason for this is not quite clear, as frozen water, 

 whether it be fresh or salt, expands to the same extent ; 

 but it is said that engineers and others who have tried 

 it are unanimous in their opinion of its value. In many 

 cases masonry has been laid in cement in cold weather, 

 a considerable proportion of salt being used in the 

 mixture. After repeated freezings and thawings it has 

 remained in perfect condition, while work near by laid 

 in mortar of the same kind, but without salt, has been 

 disintegrated by frost. We should imagine, however, 

 that dwellings constructed with salted mortar would 

 probably be damp, owing to the property salt has of 

 absorbing water. 



An Electrical Dynamometer. — A German electrical 

 engineer, Herr Zacharias, has devised an apparatus, which 

 is made by Messrs. Siemens and Halske, for automati- 

 cally recording the pressure in the mains of an electric 

 supply system. The instrument consists of an ordinary 

 pendulum clock, which every forty-five seconds closes an 

 electric contact, throwing an electro-magnet into circuit. 

 The armature of this magnet is opposed by a spring of 

 such a strength that when the pressure in the main is 120 

 volts, it occupiesa definite position. Ifthepressureincreases 

 or diminishes, the armature occupies positions to either 

 side of the normals. In front of the armature a cylinder 

 revolves slowly, carrying a paper strip with a line drawn 

 in the normal position. When the contact is made, a 

 second electro-magnet forces this cylinder against a pin 

 upon the armature of the first magnet, and by the repeti- 

 tion of this action every forty-five seconds a practically 

 continuous record of the pressure can be obtained. 



Earthquakes: — Mr. P. Malet, writing to the Morning 

 Post, combats the theory that earthquakes are always 

 dependent on volcanic action, but originate frequently 

 from submarine landslips. Mr. W. Foster, the electrician 

 of the Eastern Telegraph Company, points out that 

 soundings in the Mediterranean show mushroom-shaped 

 mountain ranges, abrupt and precipitous table-lands, 

 immense marginal shelves and over-hanging cliffs. 

 Tottering masses are close to precipices 5,000 feet deep, 

 and the action of water causes them to slide over. There 

 are instances of a difference of depth between the bow 

 and stern soundings of a ship from 300 to 12,000 feet. 

 Near Japan, on the coast of South America and in the 

 Mediterranean, earthquakes occur from these changes 

 near the shores. Sometimes disturbances take place in 

 mid-ocean, as proved by ocean waves. Hence many 

 earthquakes are the result of subsidence. We may 

 add that this theory agrees well with the observed fact 

 that in deep mines no earthquake shocks have ever been 

 observed. 



The Lake of Geneva. — It has often been asked how 

 long it would take to re-fill the lake of Geneva (Lake 

 Leman) if it were emptied. The views expressed on 

 this question are so varied — one wiseacre having affirmed 

 that it would take the Rhone only a fortnight to fill the 

 lake, whilst another has put it down at one year — that 

 an estimate just made, based upon what appears to be a 

 sound calculation, is greatly interesting, especially as the 

 result obtained will be a surprise to many. The lake of 



Geneva covers an area of 577,860,000 square metres (223 

 square miles). Its greatest depth is 312 metres (nearly 

 1,024 fset), and its average depth may therefore be 

 assumed to be 150 metres (nearly 490 feet). In accord- 

 ance with this supposition, the lake contains ninety 

 milliards of cubic metres (close upon 20,000 milliards of 

 gallons) of water. The average inflow from the Rhone 

 per second is 27 cubic metres (5,943 gallons) or 2,332,800 

 cubic metres (513,425,972 gallons) in the twenty-lour 

 hours. To fill the basin of the lake, therefore, the Rhone 

 would require — one hundred and six years. — Iron. 



New Uses for Tar. — The coating of brick and 

 wooden structures with coal tar, as a rough and ready 

 means of preserving them from the action of damp, has 

 been common from the earliest days of the gas industry. It 

 has also been usual in chemical works to protect the stones 

 used in the construction of acid tanks, etc., by a prelimi- 

 nary soaking in heated tar. But the great improvement 

 in strength and impermeability to moisture which results 

 from the simple operation of boiling bricks and stones in 

 gas tar is certainly not so generally known as it should 

 be. Professor Lunge, in the new edition of his work, 

 " Coal Tar and Ammonia," draws attention to the sub- 

 ject, and indicates several useful applications. He 

 points out that drain and roofing tiles, which are quite 

 porous and brittle as they leave the kiln, may be ren- 

 dered absolutely water tight and much stronger by im- 

 mersion in a bath of hot tar. Building stones are also 

 greatly improved by similar treatment ; and for many 

 purposes the dead black colour which results is an ad- 

 vantage rather than an objection. The tar should be 

 deprived of water and its most volatile oils ; and to pro- 

 duce good results the bath must be maintained at a 

 temperature of at least 100° C. The articles to be 

 treated should be thoroughly dried, and allowed to re- 

 main in the tar for some time. — Industries. 



The Nearest Star. — ^The distances of the stars are 

 ascertained in the same manner as these of the sun and 

 planets — that is, by parallax. Instead, however, of taking 

 two stations at different parts of the earth's surface, 

 and laying down a base line between them, we take 

 the diameter of the earth's orbit, or 183,000,000 

 miles, as the base, the observations being taken at 

 intervals of six months. Even with this immense 

 line, however, the parallax is so small that it can 

 only be detected by the most careful observations 

 and accurate instruments. In no case has it been 

 found to be greater than i"; and if this be its value, 

 the distance of the star must be 206,000 times as 

 great as that of the sun. The parallax of about a 

 dozen stars has now been ascertained, and is found 

 to vary between o-9i9" and o'046". The star a Cen- 

 tauri is the nearest to the earth, and its distance 

 is estimated at 20,496,000,000,000, or more than 20 

 billions of miles ; while the average distance of stars 

 of the first magnitude is probably three or four times 

 as great as this. These figures, however, fail to convey 

 to the mind any definite idea as to the real distance; 

 perhaps the best mode of expressing it is by stating 

 that light, with its speed of 184,000 miles a second, 

 takes 3I years to travel from that star to us ; while 

 the smaller telescopic stars are so remote that it must 

 require upwards of 5,000 years for their light to reach 

 us. — CasseWs Popular Educator. 



