208 REPORT—1863. 
Preliminary Report on the Experimental Determination of the Tempe- 
ratures of Volcanic Foci, and of the Temperature, State of Saturation, 
and Velocity of the issuing Gases and Vapours. By Ropert Mauer, 
C.E., F.R.S., F.G.S. 
Ar the Cambridge Meeting of the British Association a grant of £100 was 
made, at the joint recommendation of the Physical and the Geological Sec- 
tions, to the Reporter, in furtherance of the above-stated research. Since that 
period a like sum has been granted to him by the Royal Society of London, 
with the same object. 
The estimated cost of the investigation, as carefully calculated as the sub- 
ject admits, has been found to amount to £350—a sum which so largely ex- 
ceeds that derived from both grants, that the author felt some hesitation at 
further pursuing the matter. In view, however, of the fact that the rare 
occurrence of the peculiarly favourable form of secondary crater existing on 
Vesuvius might alter at any moment, and perhaps never again present the 
same facilities for pyrometric experiment, he resolved not to risk the oppor- 
tunity by losing further time, and to take upon himself whatever pecuniary 
risk may be involved in performing the task he has proposed, presuming that, 
should his work prove satisfactory in adding to our positive knowledge of 
vulcanology, he may be indemnified in some way for such necessary ex- 
penditure as may be incurred in excess of the two grants made. 
He has, therefore, arranged the whole of the apparatus and instruments 
required, and their construction is now in progress. These consist of the 
mechanical arrangements for suspending, passing in over, and lowering into 
the crater, and again withdrawing, various instruments of greater or less 
weight; and of the instruments themselves, both for pyrometry and for de- 
termining the velocity and state of the issuing blast of steam and gases. 
The pyrometers finally adopted consist of resistance-coils, with their various 
electrical arrangements, which are being prepared by Messrs. Siemens, 
Halske & Co., of London and Berlin, with the able assistance of the author’s 
friend Mr. Charles T. Siemens (C.E., of London); and, as a means of con- 
trol as well as of separate and distinct determination, instruments have been 
devised by the author dependent upon Peclet’s mode of determining specific 
heats. By a modification of the arrangements to be employed, the author 
anticipates being enabled to make the fused lava itself become the means of 
revealing its own temperatures at points that cannot be directly reached 
even instrumentally. The latter pyrometric instruments, as well as some of 
the suspension apparatus, are being prepared by Messrs. Siebe, engineers, of 
London. A series of thermometers and other minute apparatus are in hand, 
by Mr. Casella and by Mr. Adie, both of London. For the observation of 
the velocity of the issuing vapours and gases, the anemometer of Dr. Ro- 
binson has been modified in construction and in its metallic material, so as 
to work satisfactorily at a bright red heat ; and the instrument in this form 
has been already completed in a skilful manner by Mr. Casella. 
Of other remaining instrumental or other arrangements made or in pre- 
paration it does not seem necessary here to give any detail. The author 
expects to have everything complete and forwarded on to Naples before the 
end of 1863; and hopes to start himself for Vesuvius about the commence- 
ment of next year. 
If successful there to the extent he anticipates, he may possibly try to 
extend his observations to some other volcanic vents, more especially to 
