APRIL. 15, 1897 | 
NATURE 
571 
centres of each kathode, as shown in Fig. 13. This did not last 
for more than a second, when owing, no doubt, to the rapid fall 
of vacuum the appearance changed to that shown in Fig. 14, 
and the incandescent particles of carbon could be seen passing 
backwards and forwards along the convergent and divergent 
cones of kathode rays, which, at the lower vacuum, proceeded 
from both kathodes, and spluttering in the centre, where the 
particles going in opposite directions collided. This appearance 
lasted for some seconds, becoming gradually fainter as the vacuum 
fell. By re-exhausting the tube with the pump, however, the 
original appearance shown in Fig. 13, as also the appearance 
shown in Fig. 14, could be produced as often as desired. 
Apparently the particles of carbon become heated to incan- 
descence either by the action of the kathode rays upon them 
while they are flying through space, or by their friction in passing 
through the residual gas, and possibly by their mutual collisions, 
for in the stage shown in Fig. 14, when the kathodes themselves 
show no luminescence the flying particles appear to be most in- 
iensely luminescent when in the centre of the tube. It may be 
mentioned that after this experiment had been repeated several 
times, the glass of the tube became perceptibly blackened, 
which, taken with the fact that a similar tube with kathodes of 
aluminium showed no stream of bright particles, goes to show 
that the particles consist of carbon torn off the surfaces of the 
kathodes. J ly 
The Prodiction of X-Rays. 
In order to ascertain whether it is necessary that the kathode 
rays should fall on solid matter in order to produce X-rays, 
another tube was constructed, similar in all respects to the last, 
with the exception that the two kathodes were made of 
aluminium, 
It was thought that with this tube the opposing streams of 
kathode rays might possibly produce X-rays at the point where 
they met. This does not, however, appear to be the case, as though 
this tube, when exhausted to so high an extent that the alternative 
spark in air leapt fully eight inches, gave X-rays in considerable 
quantity, these rays appear to come entirely from portions of the 
glass of the tube that were covered with green fluorescence, and 
not at any rate appreciably from the central point between the 
two kathodes, where the opposing streams of kathode rays would 
meet one another. 
It seems, therefore, that X-rays can only be produced by 
kathode rays when these strike solid matter. 
No doubt this matter must also be positively electrified. 
THE INSTITUTION OF NAVAL ARCHITECTS. 
THE annual spring meeting of the Institution of Naval Archi- 
tects was held last week in the hall of the Society of Arts, 
under the presidency of the Earl of Hopetoun, President of the 
Institution. The meeting extended over the 7th, Sth, and 9th 
of April. The following is a list of the papers read :— 
“* Recent Trials of the Cruisers Powerful and Terrible,” by 
A. J. Durston, Engineer-in-Chief to the Royal Navy. 
‘* Water-tube Boilers in War Ships,” by Rear-Admiral C. C. P. 
Fitzgerald, RN. 
‘“A Mechanical Method of Ascertaining the Stability of 
Ships,” by A. G. Ramage. 
** On the Fighting Value of certain of the Older Tronclads if 
Re-armed,” by Captain Lord Charles Beresford, R.N. 
*“The Application of the Compound Steam Turbine to the 
Purposes of Marine Propulsion,” by the Hon. Charles Parsons. 
‘**On the Use of the Mean Water Line in designing the Lines 
of Ships,” by A. G. Ramage. 
‘<The Accelerity Diagram of the Steam Engine,” by J. Mac- 
farlane Gray. 
“© Acetylené and its Probable Future Afloat,” by Prof. Vivian 
B. Lewes. 
‘* Nickel Steel as an Improved Material for Boiler Shell Plates 
and Forgings,” by William Beardmore. 
** Application of Electrical Transmission of Power in Marine 
Engineering and Shipbuilding,” by F. von Kodolitsch. ; 
The papers were mostly of a practical rather than of a scien- 
tific interest. Mr. Durston’s contribution on water-tube boilers 
was a valuable record of the performance of the boilers in the two 
big cruisers lately added to the Navy. It may be said generally 
that the Belleville boiler has proved successful in these ships, 
and has done a little better than return-tube boilers of the type 
recently placed in the ships of Her Majesty's Navy. The fuel 
NO. 1433, VOL. 55] 
economy has been fair, 1*7 Ibs. per I.H.P. per hour ; whilst the 
weight of boiler and contained water was somewhat below that 
which has been generally reached in Navy return-tube boilers when 
run under easy conditions ; but in some cases the boiler weights per 
I.H.P. of other war vessels have been lower than the figure— 
22 I.H.P. per ton—recorded of the two cruisers. In the long 
debate which followed the reading of the paper, it was stated 
that the Belleville boiler appeared to advantage in the Powerful 
and the Zerrzb/e, because it was compared with a type of boiler 
that was ill-designed The general opinion of speakers, how- 
ever, was that Mr. Durston had scored a great success, and de- 
served to be congratulated on his courage and perseverance. 
Admiral Fitzgerald discoursed on the advantages of the Belleville 
boiler from a tactical and strategical point of view. His opinion 
was altogether favourable to the new type of steam generator. 
Lord Charles Beresford, in his contribution, advocated the re- 
arming of certain old battle-ships with modern breech-loading 
guns, or else scratching them off the list of effective ships. The 
preponderance of naval opinion appeared to be in favour of the 
latter course. Mr. Ramage’s paper described a mechanical 
method of ascertaining stability by means of wooden sections 
representing mean sections. The method is ingenious, but the 
principle is not altogether new. 
The paper by Mr. Parsons had been looked forward to with 
great interest, as it was to describe a very wonderful boat, 
which was fitted with the author’s steam turbines in place of 
ordinary engines. The 7zrébznza, as the boat is named, is 100. 
feet in length, 9 feet beam, and 444 tons displacement. The 
original turbine engine fitted in her was designed to develop: 
upwards of 1500 actual horse-power at a speed of 2500 reyolu- 
tions per minute. The boiler is of the water-tube type for 
225 lbs. per square inch working pressure with large steam 
space, and large return water legs, and with a total heating 
surface of 1100 square feet, and a grate surface of 42 square 
feet ; two firing doors are provided, one at each end. The 
stokeholds are closed, and the draught furnished by a fan 
coupled directly to the engine shaft. The weights are remark- 
able, and certainly have never before been equalled for lightness 
in any practicable marine machinery. They are as follows :— 
Main engines ... 3 tons 13 cwts. 
Total welght of machinery and boiler, 
screws and shafting, tanks, &c. ... 22 tons 
Weight of hull complete 2okS se cons 
Coal and water 74, tons 
Total displacement ... 444 tons 
The great trouble, as might have been expected from the high 
rate of revolutions, was with the screws, and Mr. Parsons has 
only repeated the experience of Mr. Thornycroft with his 
destroyer, in finding that in all screws there is a limiting 
speed of blade, due to cavitation, depending upon the slip ratio 
and the curvature of the back. In order to throw light on this 
subject, the author had recourse to an ingenious device. Model 
screws were revolved in a bath of hot water heated to within a 
few degrees of the boiling point, and in order that the model 
screw should produce analogous results to the real screw, it was 
arranged that the temperature of the water and the head of 
water above the propeller, as well as the speed of revolution, 
should be such as to closely resemble the actual conditions and 
forces at work in the real screw, the object in heating the water 
being to obtain an increased vapour pressure from the water, so 
as to permit a representation of the conditions with a more 
moderate and convenient speed of revolution than would other- 
wise have been necessary. The screw was illuminated by light 
from an arc lamp reflected from a revolving mirror attached to 
the screw shaft, the light falling on the screw at one point 
only of the revolution. The shape, form, and growth of the 
cavities could be clearly seen and traced as if stationary. It 
appeared that a cavity or blister first formed a little behind the 
leading edge, and near the tip of the blade ; then, as the speed 
of revolution was increased, it enlarged in all directions until, at 
a speed corresponding to that in the Turbinia’s propeller, it had 
grown so as to cover a sector of the screw disc of 90°. When 
the speed was still further increased, the screw, as a whole, 
revolved in a cylindrical cavity, from one end of which the 
blades scraped off layers of solid water, delivering them on to 
the other. In this extreme case nearly the whole energy of the 
screw was expended in maintaining this vacuous space. It also 
appeared that when the cavity had grown to be a little larger 
