50 Transactions. 



Before laying a cable a survey is always made along the pro- 

 posed route in order to select the most favourable ground, just 

 as the railway engineer runs lines of levels before the final loca- 

 tion of the railway. The cable engineer determines his levels 

 by means of the sounding-line (piano wire), and at the same time 

 obtains samples of the ocean-bed. It may be stated here that 

 the direct route of the Pacific cable between the stations was 

 departed from in order to avoid hills, craters, and hard or un- 

 desirable ground for the cable to rest upon. 



From the survey the number of miles (nautical) required for 

 the different sections was as follows : From Vancouver Island 

 to Fanning Island, 3,654; from Fanning to Suva, Fiji, 2,181; 

 from Suva to Norfolk Island, 1,019 ; from Norfolk to Southport, 

 Queensland, 906 ; Norfolk to Doubtless Bay, New Zealand, 513. 



The first section of the cable is about a thousand miles longer 

 than any that had been laid before. This necessitated a con- 

 siderable increase in copper for the conductor and in gutta- 

 percha for the dielectric. The working-speed of a submarine- 

 telegraph cable depends on, and is inversely proportional to, the 

 product of the total resistance of the conductor multiplied by 

 the total electro-static capacity of the core, so that, other things- 

 being equal, the speed varies inversely as the square of the 

 length of the cable. In the long section there were used 600 lb. 

 of copper and 340 lb. of guttapercha per nautical mile ; on the 

 Suva-Fanning section 220 lb. of copper and 180 lb. of gutta- 

 percha ; and on the remaining three sections the copper and 

 dielectric were in equal proportions of 130 lb. each. 



In the neighbourhood of Fiji, at a depth of 2,500 fathoms 

 a temperature of 34*1° Fahr. was noted, being the lowest tem- 

 perature taken during the survey. There is very little difference 

 in the temperature of the ocean at great depths, say below 

 3,000 fathoms, over a great extent of the earth's surface, the 

 temperature being onlv a few degrees above the freezing-point, 

 or 32° Fahr. 



The greatest depth, 3,070 fathoms (about three miles and a 

 half), was found on the Fanning-Fiji section, where the bottom 

 specimens consisted principally of radiolarian ooze. This ooze 

 is found at the greatest depths, and was obtained by the " Chal- 

 lenger's " deepest sounding in 4,475 fathoms. The United 

 States steamer " Nero " sounded in 5,269 fathoms (six miles), 

 this being the deepest sounding recorded in the ocean, and the 

 material brought from the bottom was radiolarian ooze. 



Of the 597 samples of sea-bottom obtained on the Pacific- 

 cable survey, 497 were such that they could be divided into dis- 

 tinct types of deposits. It was found that 294 samples referred 

 to globigerina ooze, sixty-five to red clay, forty-three to radio- 



