VOL. L.] I-HILOSOPHICAL TRANSACTIONS. 83 



As to the quantity of fuel, that may be saved by this method, it is not easy 

 to determine from any experiment on this engine, the boiler and fire-place of 

 which is made very different from all others, and the quantity of fuel thus greatly 

 lessened. The fire-place, which may be said to be within the boiler, and is but 

 barely large enough to contain a quantity of the roundest and strongest burning 

 coals sufficient to work the engine, cannot in this be made less; and conse- 

 quently will not admit such a saving from this model, as from one properly con- 

 structed for the purpose. 



XL Extract of a Letter, by Mr. Abraham Tremhley, F.R.S. on Earthquakes,, 

 Polypes, Fossils, &c. Translated from the French, p. 58. 



Mr. T. mentions an earthquake felt in 1756, between the Rhine and the 

 Meuse. He was also informed by Professor Donati of Turin, that a slight 

 shock had been perceived there on the 13th of August 1756, at a quarter after 

 9 in the morning. It was likewise felt in other parts of Piedmont. 



He further states, that Mons. Donati took last summer, according to his 

 custom, a journey, to prosecute his researches into natural history. He was 

 accompanied by Dr. Ascanius, f.r.s.; who was still in doubt about coral's being 

 a composition of animals. Mons. Donati carried him to the sea of Provence. 

 He ordered coral to be fished up in his presence. He placed it in a large 

 vessel full of water; and carried this vessel on shore; where he soon convinced 

 Dr. Ascanius, by his own eyes, that coral is a mass of animals of the polype 

 kind. 



Mons. Donati also wrote that he had thoroughly satisfied himself, by his last 

 observations, that the polypes are fixed to their cells ; of which he had before 

 doubted. What he says afterwards of coral appears to express with more truth 

 and precision what we ought to think of this kind of animals, than any of the 

 descriptions, which have been given since the new discoveries have changed our 

 sentiments on that subject. Polype-beds, and the cells which they contain, are 

 commonly spoken of as being the work of polypes. They are compared to the 

 honeycomb made by bees. It is more exact to say that coral, and other coral- 

 line bodies, have the same relation to the polypes united to them, that there is 

 between the shell of a snail and the snail itself, or between the bones of an ani- 

 mal, and the animal itself. Mons. Donati's words are as follow : " I am now 

 of opinion, that coral is nothing else than a real animal, which has a very great 

 number of heads. I consider the polypes of coral only as the heads of the ani- 

 mal. This animal has a bone ramified in the shape of a shrub. This bone is 

 covered with a kind of flesh, which is the flesh of the animal. My observations 

 have discovered to me several analogies between the animals of kinds approaching 

 to this. There are, for instance, keratophyta, which do not differ from coral, 



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