H. A. Rowland—Simple form of Water Battery. 147 
Advantage was taken of a natural prism to measure the indices - 
of refraction Sandy. Further, the optic axial angle was also 
obtained from a cleavage section. ‘The values obtained are as 
follows: : 
8 = 1°6104 for yellow (sodium) = 1:6075 for red (lithium). 
y= £ “ 
=e GileiG up i —IEGlas te 
2E = 126° 24’ for yellow. 
Also 2V = 67° 18’ and a = 1:6072 ealculated. 
Art. XTX.—On a Simple and Goavenient form of Water Battery ; 
by Henry A. ROWLAND. 
For some time I have had in use in my laboratory a most 
simple, convenient aud cheap form of water battery whose 
design has been in one of my note-books for at least fifteen 
years. It has proved so useful that I give below a description 
for the use of other physicists. 
- Strips of zinc and copper, each two inches wide, are soldered 
together along their edges so as to make a combined strip of a 
little less than four inches wide, allowing for the overlapping. 
It is then cut by shears into pieces about one-fourth of an inch 
wide, each composed of half zine and half copper. 
A plate of glass, very thick and a foot or less square, is 
heated and coated with shellac about an eighth of an inch thick. 
The strips of copper and zine are bent into the shape of 
the letter U, with the branches about one-fourth of an inch 
apart, and are heated and stuck to the shellac in rows, 
the soldered portion being fixed in the shellac, and the two 
branches standing up in the air, so that the zine of one piece 
comes within one-sixteenth of an inch of the copper of the next 
one. A row of ten inches long will thus contain about thirty 
elements. ‘The rows can be about one-eighth of an inch apart 
and therefore in a space ten inches square nearly 800 elements 
ean be placed. The plate is then warmed carefully so as not 
to crack and a mixture of beeswax and resin, which melts 
more easily than shellac, is then poured on the plate to a depth 
of half an inch to hold the elements in place. A frame of wood 
is made around the back of the plate with a ring screwed 
to the center so that the whole can be hung up with the zinc 
and copper elements below. t 
When required for use, lower so as to dip the tips of the 
elements into a pan of water and hang up again. The space 
between the elements being + inch, will hold a drop of water 
which will not evaporate for possibly an hour. Thus the 
battery is in operation in a minute and is perfectly insulated 
by the glass and cement. 
This is the form I have used, but the strips might better be 
soldered face to face along one edge, cut up and then opened. 
