364 REPORT—1862. 
would prevent their either being carried away bodily, or the index from being 
disturbed by unavoidable wind or still more provoking curiosity. As to the 
first point, I have gratefully to acknowledge the assistance of a large number 
of our best mountaineers, who have either deposited instruments themselves, 
or sent reports of the readings of those already placed. Thanks to their 
united efforts, about thirty minimum thermometers have been exposed at 
altitudes of from 7150 to 15,784 feet over a wide tract of country, extending 
from the summits of the Yiso, Grand Pelvoux, to the Marmolata in the South- 
ern Tyrol. : 
*(2) The correctness of the instruments was, as far as possible, secured by 
entrusting their construction to Mr. L. P. Casella, one of our best makers, and 
their uniformity by the adoption of a definite pattern. At first, in the 
absence of a good mercurial minimum capable of acting in a horizontal position, 
and in the uncertainty as to the sufficiency of the range of mercury, the 
ordinary spirit- or Rutherford’s thermometer was adopted ; but experience has 
in the great majority of cases demonstrated its inefficiency, and in consequence 
all the instruments deposited during the past summer and autumn, four in 
number, have been mercurial, of Casella’s last patent construction. 
“*(3) The question of exposure has not been solved as satisfactorily as 
could be desired, and this failure has I fear destroyed much of the value of 
the results obtained. In the first place, the process of attaching a thermo- 
meter to a bare rock at great elevations, often in a keen frost and chilling 
wind, is by no means so easy as the enthusiastic meteorologist may suppose ; 
and without discussing here the various precautions which ought to be, and 
perhaps might be, adopted in some exceptional cases, I would venture to 
express an opinion that a well-constructed cairn of sufficient elevation, so 
placed as to prevent its being buried by winter snows, is the simplest and 
most efficient means of protecting the thermometer from the most serious 
causes of disturbance. When, at least, this plan has been adopted, the 
readings of the instruments have appeared trustworthy, and in almost all 
other cases sadly the reverse. By this means also they are more screened 
from inquisitive observation, and may better escape the pilfering propensities 
of an inferior order of guides, whom we probably have to thank for the dis- 
appearance of one at least fixed very securely by the writer on the Aiguille 
du Goité. 
“A large proportion of the Rutherford minimums haye become perfectly 
useless from the division of the column, and itis this fact, coupled with a belief 
that the lowest temperature of winter on the loftiest summits rarely exceeds 
—40° Cent. (the freezing-point of mercury), which has led to their abandon- 
ment and the substitution of the mercurial construction. From some recent 
experiments, consisting in the alternate exposure of spirit-minimums to vary- 
ing temperatures, I am disposed to attribute the separation of the column to 
this cause, which, if due precautions are not observed in placing the instru- 
ment, must be especially energetic at great altitudes. 
** Unless the thermometer can be protected from the influence of radiation 
at night, or the respectively cooling and warming effects of a thin or thick 
layer of snow, variations from the true temperature of the air, amounting (as 
shown by M. Martins) to 10° or 12° Cent. (18° to 22° Fahr.), may be pro- 
duced, and the reading utterly vitiated for purposes of comparison. Besides, 
if imperfectly shielded from radiation, it will probably be more or less sub- 
jected to the direct action of the solar rays, and thus be exposed to tempera- 
tures varying within twenty-four hours by as much as 55° CG. (100° Fahr.). 
My experiments show that a much more limited range than this suffices to 
