210 
INCA TMT 
is interesting. You have seen that the ordinary zinc surface 
which has been exposed to air and moisture is quite inactive, 
but if a bright piece of zinc be immersed in water for about 
twelve hours, the surface is acted on ;, oxide of zinc is formed, 
showing generally a curious pattern. Now, if the plate be 
dried, it will be found that this oxide is strongly active, and gives 
a good picture of the markings on the zinc. The oxide evi- 
dently holds, feebly combined or entangled in it, a considerable 
quantity of the hydrogen peroxide, and it requires long drying 
or heating to a high temperature to get rid of it. Also, if a 
zinc plate be attacked by the hydrogen peroxide, the attacked 
parts become more active than the bright metal. Thus, place a 
stencil on a piece of bright zinc, and expose the plate to the 
action of an active plaster of Paris slab, or to active blotting- 
paper for a short time, then, on removing the stencil, the zinc 
plate will give a very good picture of the stencil. Any inactive 
body—for instance, a piece of Bristol board or any ordinary soft 
paper—can be made active by exposing it above a solution of 
peroxide, or, more slowly, by exposing it to a bright zinc surface. 
If, for instance, a copper stencil be laid on a piece of Bristol 
board, and a slab of active plaster of Paris be placed on the 
stencil for a short time, the. Bristol board will even, after it has 
been removed from the stencil for some time, give a good picture 
of the stencil. Drying oil and other organic bodies may be used 
in the same way to change the paper. A curious case of this 
occurred in printing a coloured advertisement cut out of a 
magazine, for there appeared printing in the picture which was 
not in the original. This printing was ultimately traced to an 
advertisement on the opposite page, which had been in contact 
with the one which was used; thus this ghostly effect was 
produced. 
I believe, then, that it is this active body, hydrogen peroxide, 
which enables us to produce pictures on a photographic plate in 
the dark, There are many other curious and interesting effects 
which it can produce, and which I should like to have shown 
you, had time permitted. 
I would only add that this investigation has been carried on 
in the Davy-Faraday laboratory of this institution. 
WILLIAM J. RUSSELL. 
THE ROYAL SOCIETY’S CONVERSAZIONE. 
‘THE second of the two annual conversazioni of the Royal 
Society was held on Wednesday, June 21, and was 
attended by a large and brilliant company. Many of the 
objects of scientific interest exhibited in the various rooms of 
the Society were the same as were shown at the first (or 
gentlemen’s) conversazione held on May 3, the most important 
of which were described in Nature of May 11 (p. 44). In 
addition to the objects already referred to, the following were 
among the exhibits. 
Mr. C. V. Boys, F.R.S., exhibited for Mr. R. W. Wood, of 
the University of Wisconsin :—(1) Silvered photographic grat- 
ing. The grating of 2,000 lines to the inch is a contact print 
on albumen. It is then silvered and polished while wet. The 
brilliancy of the spectrum is very great. (2) Diffraction colour 
photograph (see p. 199). Mr. J. E. Petavel exhibited the molten 
platinum standard of light. 
Mr. W. A. Shenstone, F.R.S., and Mr. W. T. Evans 
showed experiments on the making of tubes from rock crystal 
in the oxyhydrogen blowpipe flame. 
The Parsons Marine Steam Turbine Co., Ltd., had on view : 
(1) model of the Zrdin7a, the first vessel propelled by steam 
turbine engines ; (2) model of torpedo boat destroyer of 35 
knots guaranteed speed and 10,000 I.H_P. ; (3) model of 
Atlantic liner of 38,000 I.H.P. and 27 knots speed. 
Mr. A. A. Campbell Swinton showed experiments with 
electrolytic contact breakers. Mr. J. W. Swan, F.R.S., ex- 
hibited experiments showing effects produced by the action 
of modifications of the Wehnelt-Caldwell interrupter. Mr. 
W. R. Pidgeon showed a new influence machine. Mr. 
Mackenzie Davidson exhibited an apparatus to enable Rontgen 
ray shadows upon a fluorescent screen to be seen in stereoscopic 
relief. 
Prof. Ray Lankester, F.R.S., exhibited (1) collections of 
mosquitoes recently received at the Natural History Museum 
for study in reference to the connection of malaria with 
NO. 1548, VOL. 60] 
[JUNE 29, 1899 
mosquitoes; (2) drawings of mosquitoes, by Mr. Ernest E. 
Austen, 
Dr. Patrick Manson showed microscopic specimens showing 
the development of the parasite of malaria. 
Dr. Allan Macfadyen, for the Jenner Institute of Preventive 
Medicine, exhibited cultures and microscopical specimens of 
certain pathogenic bacteria. : 
Dr. Gladstone, F.R.S., showed ancient metals from Egypt, 
Babylon, and Britain. 
The Victoria and Albert Museum for the Seismological Com- 
mittee of the British Association exhibited a Milne horizontal- 
pendulum seismograph, with specimen of the seismograms 
yielded by it. 
Prof. Haddon, F.R.S., showed a small collection of polished 
stone implements from the Baram District, Sarawak, Borneo. 
Prof. T. G. Bonney, F.R.S., exhibited diamonds in eclogite. 
Boulders of eclogite, &c., occur in the ‘‘ Blue Ground” at the 
Newlands Diamond Mines, West Griqua Land. Two of these 
contain diamonds. Thus the diamond cannot have its genesis 
in the ‘‘ Blue Ground,” nor can the latter, ‘containing true 
boulders, be an igneous rock. 
Mr. Walter Gardiner, F.R.S., and Mr. A. W. Hill showed 
histological preparations of plant tissues demonstrating the 
‘* connecting threads” which traverse the cell walls and establish 
a means of communication between the several cells. 
Dr. F, W. Oliver exhibited a collection of Cingalese 
Podostemaceze. The specimens included the majority of the 
eugealcse representatives of this remarkable family of flowering 
plants. 
THE RED SPOT ON JUPITER. 
HAVE frequently observed this object during the present 
apparition of the planet, but always found it exceedingly 
faint and only visible under good definition. Its aspect is that 
of a faint dusky stain attached to the northern side of the 
south temperate belt, and partially filling up the hollow formed 
in the great southern equatorial belt. With my 10-inch re- 
flector—power 312—the following estimated times of transit 
were obtained, and I have added the corresponding longitude of 
the object :— 
Date. Transit time. Long. 
h. m. ib 
1898 November29 _... 19 55 31°9 
1899 February 2 18 39 29°5 
7 17 46 29'0 
24 16 49 300 
26 18 27 29'9 
April 19 II 20 32°0 
26 12) 33 30'8 
May 6 10 19 Siu, 
8) pire II 58 32°3 
ime 4s 9 18 34°4 
6. ces 10 57 34'8 
9 8 26 34°4 
II IO 4 a 34°0 
14 7 32 os 329 
16 O13.) cs BANA 
21 8 20 ae 33°5 
2g 958 Ne 33:1 
26 72 ee 33°7 
This feature has shown a remarkable variation of motion during 
the last twelve months. In the winter there was a very decided 
acceleration of speed, but during the past three months the 
motion has been again retarded. The acceleration was first 
noticed here on the morning of February 3, when the marking 
came to the central meridian seven or cight minutes before its 
computed time. In the first half of 1898, and again during 
the last few months, the rotation period of the spot was nearly 
gh. 55m. 42s., but for several months in the past winter the rate 
corresponded very nearly with gh. 55m. 40°6s., the period 
employed by Mr. Crommelin in System II. of his ephemerides 
(Monthly Notices, November 1898). But, unfortunately, the 
precise character of the recent irregularity of motion cannot be 
determined, Jupiter having been too near the sun for effective 
observation during several months (August to November 1895). 
