82 Miscellaneous. 



" 5. Observations on the Saline, Mineral, and Organic Constituents 

 of the water from the surface downwards. 



" 6. Observations, when practicable, on the Penetration of Light, 

 and on the effects of immersion at great depths of the various 

 substances employed as Coatings for Telegraphic Cables. 



"7. Natural Histor}^ generally. 



" 8. And, lastly. Meteorological Observations, when bearing on 

 any of the above conditions. 



" With reference to the first of these heads (namely, soundings for 

 depth, &c.) I may state that it ought to be regarded as an object of 

 primary importance to probe* the deposits of the sea-bed in every 

 instance in which circumstances engender a suspicion that they are 

 merely superficial films resting vipon otherwise uncovered rocky or 

 * stony surfaces. That such surfaces occur in some portions of the 

 ocean I think there is no just ground to doubt ; and where they 

 occur I would suggest that an endeavour should be made to avoid 

 them by searching out a detour, if discoverable within certain limits ; 

 or, if unavoidable owing to their great extent, that measures should 

 be devised for the strengthening or support of that portion of the 

 telegraphic cable which traverses them. 



" I would observe that, hitherto, the bringing-up in the sounding- 

 machine of a few grains, or even the fraction of a grain, of soft 

 deposit, has been accepted as evidence that the bottom is composed 

 of soft material, and not of rock, as it may unquestionably be not- 

 withstanding. 



" The observations under the second head (namely, the nature of 

 the deposits) demand no comment beyond allusion to their direct 

 bearing, when taken in conjunction with the ascertained depths, on 

 the formation of sedimentary or concretionary strata, and the 

 evidences of their alternate upheaval and subsidence. 



" Those under the third head require a word or two of explanation. 



" Although the temperature of the ocean, from the surface down- 

 wards, has been most ably elucidated by the late Sir James Eoss in 

 the southern hemisphere, it has not, so far as I am aware, been 

 ascertained with equal exactitude to the north of the Equator ; nor 

 has the law which regulates the equalization of that temperature 

 along the same parallels of latitude at a certain depth below the 

 surface been clearly established. Accordingly, every additional 

 observation and fact which throws light on the mutual operation of 

 terrestrial heat and surface-radiation on the waters of the ocean 

 must prove of value in a scientific point of view, and must exercise 

 a direct influence on the permanent safety of a submerged cable. 

 But, irrespectively of the general law regulating the temperature of 

 the ocean, it is by no means improbable that deep-seated tracts of 

 water exist, along which the temperature may be materially in- 

 fluenced by submarine action. Although no direct data have here- 

 tofore been elicited which would lead to the suspicion that any 

 portion of the route likely to be passed over between Ireland and 



* An instrument for effecting this purpose (together with mj' other 

 instruments) was exhibited by me at the meeting of the Geographical 

 Society, .January 12, 1863. 



