TRANSACTIONS OF THE SECTIONS. 



27 



sea pressure-gauge, in order to supply any correction required for variation of the 

 volume of water in it through change of temperature. 



However, it has been suggested by Captain Davis that, to render this instrument 

 independent of this calculation, it should be placed previous to use in water of 

 about the temperature of the air, so as to acquire this temperatiu-e, aud the same 

 action repeated after use and before reading off. 



Variation in the Volume of Sea- Water, boiled to free it from air, with chano-e 

 of temperature. Thermometer 67°'5 Fahr. Barometer 29-92 inches. 



RemarTcs on a new Telemeter ; a neiu Polanmeter ; a new Polarizing Micro- 

 scojne ; and various Spectroscopes. By M , Hofmann, 



On the North Atlantic Telegraph. Bij Jf. J. Holmes. 



The author described a projected liue of telegraphic commimication between 

 England and Ameiica via Scotland, the Faroe Isles, Iceland, Greenland, and the 

 coast of Labrador, and known as the North Atlantic Telegraph. A glance at the 

 map in the direction pointed out will at once show that convenient natural landino- 

 stations exist, breaking up the cable into four shoi-t lengths or sections. Not only 

 wUl this subdivision of the cable diminish mechanical risks in submero-ino- but the 

 retardation oflered to the passage of the cim-ent through the several short sections 

 IS almost as nothing when compared with that of an unbroken length of 2000 

 ™r®- J^*',^^'^^'^S'f "ieP*^ of ^^^e ocean between Scotland and the Faroe Isles is 

 only loO fathoms, the greatest depth 683 fathoms. Between the Faroes and Ice- 

 laud 2.o0tathoms,_with about the same maximum depth. Between Iceland and 

 Jidian,shaab, the intended landiug-place of the cable iu Greenland, the greatest 

 deptli 13 lo50 fathoms ; and between Greenland and Labrador rather over 2000 

 fathoms. These lengths of cable and depths of ocean are both not only manage- 

 able but practicable, and no difficulties iu the working exist that are not akeady 

 known by reference to the practical working of existing cables imder the conditions 



* The volume at 86° being considered as unity, and divided into 20,000 parts. 

 itsU^Tnf^t28'•^ ^^''"' '''^"'^'*'' temperature of the sea-water has prevented 



