302 Proceedings of Royal Society of Edinburgh. [sess. 
§ 8. In order to be able to adjust the quantity of air in the bulb 
■while filling it, a small capillary, E, is drawn out from the side of 
the stem at a point near the volume mark. This allows the air to 
escape as the mercury is introduced. The capillary is sealed before 
the reading of the pressure at 0° C. is taken. 
§ 9. It would be possible to give the thermometer a greater ap- 
parent simplicity by omitting the auxiliary reservoir and making 
the pressure - tube movable, as in Joly’s thermometer. The 
simplification is more apparent than real, however, and introduces 
several disadvantages. It does not do away with external pres- 
sure, as that will have its influence on the flexible connecting-tube. 
It would also be impossible to graduate the pressure-tube itself, and 
hence the objectionable arrangement of a scale on a mirror behind 
the tube would have to be used. The clamp which supported the 
main tube would also have to be in a more inconvenient position 
than that for the reservoir in the form in which I have described 
(see fig. 2). 
