268 Bulletin of Laboratories of Denison University. [Voi. xi 
satisfaction. High sensitiveness requires a very fine capillary, 
of perhaps .02 mm. diameter. So fine a capillary is easily 
clogged by a minute particle or breaks develop in the mercury 
column which hours of labor sometimes fail to remove. I have 
had one which showed a deflection with .00005 volt; another 
moved 1-5 mm. (375 divisions on micrometer head) with a 
potential difference of .001 volt. But neither of these remained 
long in good working condition. 
A series of nerve-trying experiences with Ostwald’s third 
type led me to seek some modification which would be highly 
sensitive and at the same time keep in working order fairly well 
and be capable of restoration to a sensitive condition if by 
chance injured through misuse. This was found at length in a 
modification of a simple form described by Paschen. On read- 
ing his paper (Wied. Ann. Vol. 39, p. 43) I noticed that he 
reached a fair degree of sensitiveness in a form of instrument 
in which the capillary, (if such it can be called) was of relatively 
huge dimensions (3 mm. in diameter). His arrangement is 
shown in Fig. 4. The capillary is one of the limbs of a U-tube. 
In his instrument one limb was 24 mm. in diameter the other 
three. As the sensitiveness of the Lippmann and Ostwald 
forms is nearly inversely proportional to the size of the capil- 
lary, it was natural to suspect that a reduction in size of the 
smaller limb to moderate capillary dimensions would exalt the 
sensitiveness sufficiently and still avoid the exasperating tend- 
ency to clog and stick that inheres in Lippmann’s or Ostwald’s 
third form. This proved to be the case. 
A number of Paschen instruments were constructed with 
capillary limbs of varying size. One similar in dimensions to 
his gave rather low sensitiveness, but as the capillary was made 
smaller the sensitiveness increased as shown by the following 
table : 
Tube Diam. of Capillary Deflection for .001 volt 
I 
3.70 mtn. 
.0018 mm.= 
3.6 divisions 
2 
1.32 
.0038 
7.3 
3 
1.05 
.0092 
18. 
4 
•51 
.0117 
23- 
5 
•31 
•0255 
50- 
6 
.21 
.0765 
150. 
7 
.16 
.0260 
51 - 
