LL. Waldo— Papers on Thermometry. 59 
plane, and can be placed at varying distances from each other 
in order to bring the two ends of the column of mereury used 
in calibration into view at the same time. 
III. A small vertical cathetometer by Wm. Grunow, grad- 
uated upon its vertical triangular bar to single millimeters and 
read by a vernier direct 0-2™; 0:05" can be readily 
estimated. The graduation extends over 220™. The telescope 
is provided with an objective of 4 inches focal length by Beck 
and an eye-piece micrometer by Rogers. The smallest division 
of the eye-piece micrometer subtends an apparent angle of 39 
minutes, and the telescope magnifies 20 diameters at the dis- 
tance at which it is commonly used.’ The vertical motion of 
the telescope is by means of a rack and pinion. 
IV. The standard barometer, “Jas. Green, N. Y., 957.” 
base is 1:60 inches. The vernier reads by estimation to 0-001 
inches, and the scale is set about 0°01 inches lower than the meas- 
ured height above the ivory point which is adjusted on Fortin’s 
principal at the base, in order to correct for capillarity of the 
tube. The length of the brass tube is expressed in terms of 
the standard United States Coast Survey yard, to within any 
errors appreciable in its readings. It read within 0-001 inc 
of the standard barometer kept by Mr. Green as representing 
the standard of the Kew Observatory, in October of this year 
After comparison it was carefully transferred to New Haven 
by hand, and since that date has been hung at the level of the 
boiling-point apparatus to be described. The attached ther- 
mometer has a correction of —0°-2 at the freezing-point, and 
of —0°-7 at 80° F. The barometer from the cistern upward is 
wrapped in cotton-wool to keep the temperature as constant as 
possible and to insure an accurate determination of it by means 
of the attached thermometer. 
_ V. The freezing point apparatus, which consists of a tinned 
Iron vessel within another, the space between them filled with 
cotton wool. The inner vessel holds two liters of melting snow 
or ice. There is provision for the escape of the water into a 
‘ ace at the bottom of the inner vessel, protected from -radia- 
ion. 
mo 
VI. A boiling-point apparatus constructed of brass after 
Regnault’s plan. The diameter of the inner steam chamber is 
13™, and the apparatus is provided with a water manometer to 
keep the pressure constant. 
VIL. A boiling-point apparatus, constructed entirely of glass, 
with a single steam chamber extending to a height of 71™ 
above the surface of the boiling water. A water manometer 
