ent of water, and records its
temperature. It is graduated by immersing the instrument in known and
constant temperatures, and thus the graduations on the thermometer give at
once the temperature, not of the current of water, but of the medium from
which it has received its heat. In order to render the instrument
perfectly reliable, all that is necessary is that the current of water
should be always perfectly uniform, and this is easily attained by fixing
the size of the outlet once for all, and also the level of water in the
tank. So arranged, the pyrometer works with great regularity, indicating
the least variations of temperature, requiring no sort of attention, and
never suffering injury under the most intense heat; in fact the tube, when
withdrawn from the furnace, is found to be merely warm. If there is any
risk of the instrument getting broken from fall of materials or other
causes, it may be fitted with an ingenious self-acting apparatus shutting
off the supply. For this purpose the water which has passed the
thermometer is made to fall into a funnel hung on the longer arm of a
balanced lever. With an ordinary flow the water stands at a certain height
in the funnel, and, while this is so, the lever remains balanced; but if
from any accident the flow is diminished, the level of the water in the
funnel descends, the other arm of the lever falls, and in doing so
releases two springs, one of which in flying up rings a bell, and the
other by detaching a counterweight closes a cock and stops the supply of
water altogether.

It will be seen that these instruments are not adapted for shifting about
from place to place in order to observe different temperatures, but rather
for following the variations of temperature at one and the same place. For
many purposes this is of great importance. They have been used with great
success in porcelain furnaces, both at the famous manufactories at Sevres
and at another porcelain works in Limoges. From both these establishments
very favorable reports as to their working have been received.--_W.R.
Browne, in Nature_.

* * * * *

[NATURE.]

THE TEMPERATURE OF THE SOLAR SURFACE.

I have, during the summer solstice of 1884, carried out an experimental
investigation for the purpose of demonstrating the temperature of the
solar surface corresponding with the temperature transmitted to the sun
motor. Referring to the illustrations previously publis