The Rev. F. J. H. Wollaston on the 
304 
with an adjustment by a screw at the top. The vernier is 
applied to the edge of the scale. I recommend that in mak- 
ing these thermometers, the bulb be blown on a piece of tube 
of -§- inch bore, or nearly, so that the mercury expanded be- 
fore boiling may be wholly contained in that tube without 
requiring an upper bulb ; for if that bulb be made of a size 
to allow the mercury to separate in it, a globule may lodge 
in the upper part of it near the fine thread, and be attended 
with much inconvenience. 
To protect the lamp from wind more effectually than was 
done by the small tent-stand formerly described, I have 
made the outside case of thin copper, hard soldered, so as to 
serve as a lanthorn to contain the lamp burning at bottom ; 
while the boiler, which is made of a drawn tube, with the 
thermometer, slips down from above, and is also protected 
from the cold air during the experiment. The inverted 
boiler screws as before, over the scale of the thermometer, 
and packs in the centre of the case for carriage, the bulb of 
the thermometer going downwards into the chimney of the 
lamp ; round the chimney in the lower part of the case, is 
space sufficient for stowing some matches of the oxymuriate 
of potash, a bottle of sulphuric acid, a wax candle, a tin 
bottle of water, a pair of scissors for trimming the lamp, a 
turnscrew and thermometer. In the upper part is also room 
for some tow or rag for cleaning, & c. ; and the whole, when 
packed for use, weighs two pounds. Still farther to be 
guarded against wind, if necessary, I carried, as a walking- 
stick, a rod cut into three, and jointed at top, which belongs 
to a theodolite as its stand ; and had in my pocket a conical 
bag of thin cotton, which would cover the whole as a tent* 
