530 G. Poulett Scrope — The Mechanism of Stromholi. 



Mr. Mallet's own observations are obscured by a singular amount 

 of incorrectness in the measurements given by him as taken with 

 the aneroid, which not only err to the extent of more than a hundred 

 per cent., but are also wholly inconsistent with the sectional dia- 

 grams by which the text is illustrated. Lest I should be supposed 

 rashly to dispute Mr. Mallet's professional ability in the measure- 

 ment of heights and the construction of diagrams, I annex an 

 accurate copy of his principal diagram representing the island, with 

 the heights as given by him in the text placed alongside (Fig. 1). 



Fig. 1. 



A glance at this figure is sufficient to show that, if Mr. Mallet's 

 estimate of the extreme height of the mountain, viz. 2,843 feet, be 

 correct (the English and French Admiralty Charts, however, give 

 it at 3,090 feet), all the other heights in the diagram must be at 

 least 1,000 feet below the truth; — the point C, for example, being 

 visibly about three-fourths of the whole height of the mountain, and 

 therefore about 2,143 feet, instead of 1,200, which Mr. Mallet says he 

 found it. All the lower points are in error to the same amount or 

 more. Mr. Mallet's diagTam, however, is not so far wrong as the 

 measurements given in his text, since the best authorities concur in 

 stating the height from the sea of the upper lip of the crater (C in 

 the diagram) as about 2,200 feet, instead of 1,200 only, which Mr. 

 Mallet assigns to it. It might be supposed that the several heights 

 given in the text are, by a typographical error, made 1,000 feet less 

 than the author intended. But this is inadmissible, not only on account 

 of their number, but because (as will be shortly shown) Mr. Mallet's 

 whole theory hangs upon the proximity of the bottom of the crater, 

 marked E, to the sea-level, estimated by him as only 300 feet in 

 vertical distance, whereas in fact it is nearly if not quite 2,000 ! 



In correction of these errors of Mr. Mallet, I give the following 



from the highest authorities : — 



Extreme Height of the Mountain. 

 By Frencli Admiralty Chart (Dumondeau) 942 metres ( = 3,090 feet). 



By Enfjlish Admiralty Chart 3,090 feet. 



By Italian Government Map 921 mStres ( = 3,022 feet). 



By Hoffmann (Barometrical measurement) 



confirmed by Abich 2,775 German feet ( = 2,853 English feet). 



The latter measurement agrees, it will be seen, very closely with 

 that of Mr. Mallet ; not so the following, which is far more im- 

 portant, having a direct bearing upon the structure of the mountain, 

 and especially on Mr. Mallet's theory of its phenomena. 



