726 THE POPULAR SCIENCE MONTHLY. 



The scene here described corresponds pretty closely, I have little 

 doubt, with one actually witnessed by the novelist, except only that 

 the captain or chief officer made the observations, and that either 

 there had not been ten days' murky weather, or else that in the fore- 

 noon, several hours at least before noon, an observation of the sun had 

 been made. The noon observation would give the latitude, and, com- 

 bined with a forenoon observation, would give the longitude, but 

 alone would be practically useless for that purpose. It is curious that 

 the novelist sets the longitude as assigned much more closely than the 

 latitude, and the value given would imply that the ship's time was 

 known within less than a second. This would in any case be imprac- 

 ticable ; but, from noon observations, the time could not be learned 

 within a minute at the least. The real fact is, that, to determine true 

 time, the seaman selects, not noon, as is commonly supposed, but a 

 time when the sun is nearly due east or due west. For then the sun's 

 elevation changes most rapidly, and so gives the surest means of de- 

 termining the time. The reader can easily see the rationale of this by 

 considering the case of an ordinary clock-hand. Suppose our only 

 means of telling the time was by noting how high the end of the min- 

 ute-hand was : then, clearly, we should be apt to make a greater mis- 

 take in estimating the time, when the hand was near XII., than at any 

 other time, because then its end changes very slowly in height, and a 

 minute more or less makes very little difference. On the contrary, 

 when the hand was near III. and IX., we could in a very few seconds 

 note any change of the height of its extremity. In one case we could 

 not tell the time within a minute or two ; in the other, we could tell it 

 within a few seconds. 



But the noon observation would be wanted to complete the deter- 

 mination of the longitude ; for, until the latitude was known, the cap- 

 tain would not be aware what apparent path the sun was describing 

 in the heavens, and therefore would not know the time corresponding 

 to any particular solar observation. So that a passenger, curious in 

 watching the captain's work, would be apt to infer that the noon ob- 

 servations gave the longitude, since he would perceive that from them 

 the captain worked out both the longitude and the latitude. 



It is curious that another and critical portion of the same enter- 

 taining novel is affected by the mistake of the novelist on this subject. 

 After the scuttling of the Proserpine, and other events, Hazel and Miss 

 Rolleston are alone on an island in the Pacific. Hazel seeks to deter- 

 mine their position, as one step toward escape. Xow, " you must 

 know that Hazel, as he lay on his back in the boat, had often, in a 

 half-drowsy way, watched the effect of the sun upon the boat's mast : 

 it now stood, a bare pole, and at certain hours acted like the needle of 

 a dial by casting a shadow on the sands. Above all, he could see 

 pretty well, by means of this pole and its shadow, when the sun at- 

 tained its greatest elevation. He now asked Miss Rolleston to assist 



