F Sadi 
L. Waldo—Papers on Thermometry. 447 
The advantage of this form of air thermometer is that the 
whole of the apparatus is at the temperature of the comparator, 
and is placed in a medium which will give us with great pre- 
cision the temperature of the mercury in the air thermometer 
tubes. The corrections for the air contained in the capillary 
time to satisfy myself that we reach very nearly the same 
results as Professor Rowland has done before us. In a subse- 
scientific men. 
The general characteristics of the above classes of thermom- 
eters may be described as follows : 
Designation. Characteristics. 
1. Kew standards, Thick stems, medium sized cylindrical bulbs blown 
from a separate piece of glass and joined to the ther 
the same pot as t 
composed. Flint glass known as ‘‘ Powell’s best flint.” 
2. Fuess standards. Thin stem, small cylindrical bulbs blown from the 
same glass. Detached porcelain seale. Glass unknown. 
3. Tonnelot standards. | Medium stem, long cylindrical bulbs blown from the 
same glass. The comparison with the Johns Hopkins 
Baudin thermometers shows the glass to be practically 
the same in both. 
From a consideration of the above comparisons we reach the 
following conclusions : . 
1 Kew standards made from the glass known as “Pow- 
of the Kew standards 578 and 584 are very nearly coincident 
with the air thermometer between the freezing and boiling 
points of water; the maximum correction not exceeding 
~0°-05 C. and reaching its maximum probably in the vicinity 
of 60° C.. 
9. The Fuess standards have a maximum correction — of 
about —0°-20 ©., which oceurs at a point beyond the 50° point. 
* Jas. Powell & Sons, Whitefriars Glass Works, Temple street, E. C., London. 
I have written to these gentlemen for the chemical constitution of this glass, but 
they are unwilling, presumably from. business reasons, to state the proportions 
d in its manufac 
