ange in the apparatus rendered it suitable for the new
conditions, but time does not permit me to describe the arrangements in
detail. It is, however, less necessary to do so as the method is in all
essentials the same as that described in this room two years ago by Lord
Rayleigh in connection with the photography of a breaking soap-film.[4]
I therefore pass at once to the photographs themselves.

The first two series (X. and XI.) may be described as shadow
photographs; they were obtained by allowing a drop of mercury to fall on
to the naked photographic plate itself, the illuminating spark being
produced vertically above it, and they give only a horizontal section of
the drop in various stages, revealing the form of the outline of the
part in contact with the plate, but of course telling nothing about the
shape of the parts above. The first series corresponds to a mercury
splash very similar to that first described, and the second to the
splash of a larger drop such as was not described. In each series, the
tearing of the thin central film to which allusion was made is well
illustrated. I think the first comment that any one would make is that
the photographs, while they bear out the drawings in many details, show
greater irregularity than the drawings would have led one to expect. On
this point I shall presently have something to say.

SERIES X.

(1) _Instantaneous Shadow Photographs (life size) of the Splash of a
Drop of Mercury falling 8 cm. on to the Photographic Plate._

[Illustration: 1

Actual size of the Drop, 4.83 mm.]

[Illustration: 2

[Tau] = 0]

[Illustration: 3]

[Illustration: 4]

[Illustration: 5]

[Illustration: 6]

[Illustration: 7

[Tau] = .048 sec.]

SERIES XI.

(2) _Instantaneous Shadow Photographs (life size) of the Splash of a
Drop of Mercury falling 15 cm. on to Glass._

[Illustration: 1

Actual size, 4.83 mm. in diameter.]

[Illustration: 2

[Tau] = 0 sec.]

[Illustration: 3]

[Illustration: 4

4A

[Tau] = .0032 sec.]

[Illustration: 5

[Tau] = .0063 sec.]

[Illustration: 5A

[Tau] = .0094 sec.]

[Illustration: 6

[Tau] = .0134 sec.]

Comparing the first set of drawings (pp. 20-24) with the photographs of
Series X., it will be seen that

Photograph 2 corresponds to drawing 4 or 5
" 3 " " 9
" 4 " " 18
" 6 " " 20
" 7 " " 24