Serial Soundings and Temperature Curves. 35 



the surface to 100 fathoms, every 25 fathoms down to 300 

 fathoms, and every 100 fathoms down to 1000 or 1500 fathoms, 

 furnishes, with the addition of the bottom-temperature, sufficient 

 materials for scientific enquiry ; and, although it may be secured 

 in the course of a few hours, it can only be accomplished under 

 favourable' conditions of weather. The number of serial sound- 

 ings obtained by H.M.S. "Challenger" during her three and 

 a-half years' cruise amounts to about 260, of which 120 belong 

 to the Atlantic, 1 10 to the Pacific, the remainder beinof about 

 equally divided between the Southern Ocean and the seas of 

 the Indian Archipelago. An important series of soundings was 

 taken almost simultaneously by the officers of the Imperial 

 German frigate the " Gazelle," whose operations in the Indian 

 Ocean and in the south-western portion of the Pacific, not visited 

 by H.M.S. "Challenger," form a valuable supplement to the 

 results obtained by the officers of the English expedition. 



When recording the observations made at a particular station, 

 it becomes at once apparent that a mere tabulated statement of 

 the temperature registered at each depth is but an imperfect mode 

 of exhibiting the results of the soundings, and recourse is had to 

 the method of curves. It is not necessary here to insist on the 

 evident advantages of this method of representing graphically 

 the various stages of a phenomenon under observation, and on 

 the facilities which it offers not only for seizing at a glance its 

 leading features, but also for detecting the errors of the instru- 

 ments employed and those of the observer himself. 



To convert a tabulated statement of a series of temperature 

 observations belonging to one station into a curve, it is sufficient 

 to lay down a scale of fathoms, say along a horizontal line, and, 

 at right angles to the latter, a scale of degrees of temperature 

 (Figs. 1 to 10). At the points on the horizontal scale corre- 

 sponding with the depths at which the observations were taken, 

 perpendicular lines are drawn, and their lengths made equal to 



