Hints for the Formation of a Theory of the 'Earth. 2^9 



fail to be of eflential fervice to him. This faft I can atteft 

 from experience. 



If abfohite precifion be wanted, it may be obtained by 

 employing three or more pyrometers, diftributed at regular 

 diftances round the furnace, inftead of ufing only one. The 

 mean of the whole will be the true degree of heat in the 

 furnacci 



VII. Agenda^ or a CoUeBion of Obfervations and Refearches 

 the Refults of which may ferve as the Foundation for a, 

 Theorj of the Fcrth. ^ M. De SauSSUjiE. 



[Continued from page 190.'] 

 CHAP. XVlli. 



A. Ohfcrvaiions to be made on Volcanoes at the Time of an 



Fruption. 



T ' . 



I- J- HE form, dmienfions, and elevation of the crater. 



2. the colour, elevation, and other fenfible qualities of 

 the flames and the fmoke. 



3. Phenomena which preceded the eruption, fubterranean 

 rioife, earthquakes, extraordinary movements of the fea. 



4. Phenomena which accompany the eruption ; as thun- 

 der, lightning, pofitive or negative eleftricity, fubterranean 

 hoife, earthquakes: fcorije, afhes, and ftones thrown up; to 

 Svhat height and diftance. 



5. Smell of the fmoke. In general it indicates the ful- 

 t)hureous acid; but it may indicate alfo bitumen and coal. 



6. Nature of the gafes which efcape during the eruption. 



7. Velocity of the lava. Its degree of fluidity compared 

 Kvlih the inclination of the ground over which it flows. 



8. To meafure, if poilible, the degree of its heat when it- 

 iflucs from the volcano. 



f. Whether the lava appears to be in a ftate of combuf- 

 tiouj or only incandcfcence. 



S a 10. Wbe- 



