86 
NATURE 
| NovEMBER 22, 1906 
Ephemeris 12h. Berlin. 
1906 a (true) § (true) | 1906 a (true) 6 (true) 
m, Ss. - Fal h. m. s. 3 F 
Noy. 20... 10 055 ... 24 28°1| Nov. 28... 10 41 34 ... 34 106 
BAverIO2OIR Ths 29 247\)Dec. a2 een is ie Song ons 
The brightness of this object is now decreasing, and 
will be 1-04 times that at the time of discovery on 
November 24, when its magnitude was 8-5 (Kiel Circular, 
No. 92). In announcing the discovery of this comet last 
week, it was stated that the magnitude was not given in 
the Kiel telegrams. Prof. Kreutz writes to point out that 
the magnitude was given; and we regret that the group of 
figures containing it was mistranscribed whilst decodifying 
the message. 
Hatiey’s Comet.—In vol. exv., part v., of the Sitsungs- 
berichte dey kaiserlichen Akademie der Wissenschaften, Dr. 
J. Holetschek discusses the probable time at which Halley’s 
comet may be looked for with reasonable chance of success 
during its forthcoming return. By reason of a particular 
combination of perturbations, the present period of reyolu- 
tion (743 years) is the shortest observed since 1531, but 
after determining the comet’s distance from the earth and 
the sun during the oppositions of 1906-9, Dr. Holetschek 
concludes that there is no great likelihood of this object 
being re-discovered before the latter part of 1908. At the 
end “of 1909 it should certainly be easily observable, and 
during the second half of March, 1910, it should become 
a naked-eye object. According to the elements published 
in the Connaissance des Temps (1900), the comet is due to 
pass through perihelion on May 16, 1910. 
A Bricur Metror.—An exceptionally bez autifal meteor 
was observed by Mr. Rolston at the Solar Physics Observ- 
atory, South Kensington, at 13h. 26-5m. on Navenber 17. 
The approximate positions of the beginning and end of the 
trail were a=753°, Batiste and a=88°, 6=+14°, re- 
spectively. The narrow, fan- shaped head "was nearly as 
bright as Jupiter, and left behind it a shimmering trail of a 
reddish colour, similar in appearance to the shower of 
sparks which come from a suddenly-braked train wheel. 
The duration of the meteor’s flight was little more than 
one second, and the trail died away immediately. 
Tue Unitep States Navat OpseERVATORY PUBLICATIONS. 
—We have received from the U.S. Naval Department a 
copy of part iv., vol. iv. (second series), of their Publi- 
cations, containing, in addition to a profusely illustrated 
account of the 1900 and igor eclipse expeditions, previously 
described by Dr. W. J. S. Lockyer (Nature, vol. Ixxiii., 
p- 486, March 22, 1906), a number of tables for use in the 
reduction of astronomical observations. The reduction 
tables for transit-circle observations contained in part ii. 
are only suitable for the Naval Observatory, with the ex- 
ception of the refraction tables, which are based on the 
Pulkowa values. 
Part iii. contains reduction tables for equatorial obsery- 
ations, including those for differential refraction and instru- 
mental corrections. In part iv. there is a very interesting 
discussion of the present status of the use of standard 
time, in which a fairly complete account of the standard 
times in use in every part of the earth is given. 
The conversion tables, and the summaries of the time 
in each country, giving the standard meridians and the 
relation to the standard times of other countries, should 
prove very useful for reference purposes. 
THE ACTION OF TRAM-CAR BRAKES. 
TE AT steep gradients can be overcome by mechanically- 
propelled tram-cars—as compared to ordinary railway 
trains—and that street-cars are driven on public thorough- 
fares, more or less crowded with other traftic, renders 
the brake question one of considerable importance. The 
lamentable accident that occurred at Highgate last June 
affords strong evidence of this. On June 23 a double-deck 
bogie car became unmanageable, and ran at a great pace 
for a distance of about three furlongs down the hill extend- 
ing southwards from Highgate Archway to the Archway 
Tavern. The gradients here, though considerable, are 
not excessive for tramway work when the cars are 
NO. 1934, VOL. 75]| 
-to the driving wheels, 
operated with due care. The lines have an inclination of 
about 1 in 223 on the hill, but in other parts of the line 
the gradient is 1 in 18, whilst gradients of 1 in 9 have 
been authorised. Colonel Yorke, to whose full and 
admirable report on the accident we shall make frequent 
reference, has said that the Board of Trade insists on 
track brakes being fitted to all cars running over gradients 
of 1 in 15, the speed being limited to six miles an hour. 
Of the passengers on the car, only a few were slightly 
injured, but three persons in the street were killed and 
twenty were injured, some seriously. The runaway car 
collided with a hearse, a furniture van, a motor-omnibus, 
and another van, being finally brought to rest by a 
stationary car at the terminus. The chief lesson to be 
gained from the disaster is connected with the action of 
brakes on vehicles of this description. 
The car would carry thirty passengers inside and thirty- 
eight on the top. It was of the double-bogie type, with 
eight chilled cast-iron wheels and maximum-traction 
trucks, the small wheels leading. There was a 35-h.p. 
motor on each bogie truck, the motors being geared to 
the axles of the large driving wheels. The general design 
appears, from the descriptions given in Colonel Yorke’s 
report, to be of a well-known type in which the effort is 
made to get the maximum weight for adhesion on the 
driving wheels without the use of a motor on each axle, 
the latter being an arrangement which, with a double- 
bogie car, would need four motors. With this design the 
distribution of weight becomes a matter of great import- 
ance. The car in question weighed twelve tons unladen, 
and the engineer to the owners, the Metropolitan Electric 
Tramway Company, has estimated that four tons were 
carried upon each of the driving axles, and two tons upon 
each of the pony axles. 
The car had hand brakes, of the usual description, 
working brake blocks on all eight wheels, and was also 
fitted with electromagnetic track brakes having two shoes 
on each bogie. There were also four sand-boxes operated 
from the driving platform. 
The track brake has been introduced at a comparatively 
recent date, and is especially for tramway work. Its 
failure to stop the car in the instance under consideration 
is therefore a circumstance worthy of close inquiry. There 
are two leading descriptions of electromagnetic track brake 
or slipper brake, but Colonel Yorke’s report does not 
specify the type fitted, although the description fairly 
well indicates which was used. There are certain 
features common to both types, and each acts by the 
brake shoes being strongly attracted to and pressed on the 
rails by magnetic force. The magnets formed by the brake 
shoes are energised by current generated by the car motors. 
Colonel Yorke gives a concise description of the brakes 
on the car under notice. Each brake shoe consisted 
of two narrow steel plates 15 inches long, placed side 
by side, with a small interval between them, thus form- 
ing the poles of a powerful electromagnet, excited by 
current supplied by the motors acting as generators. The 
shoes of the brakes in question were also connected to 
the brake blocks which formed part of the hand brakes, 
so that the latter pressed against the wheels, and there- 
fore automatically came into play when the track brakes 
were applied. This is a usual arrangement. With electro- 
magnetic brakes of this description there is a retarding 
action due to the motors running as generators, and there- 
fore putting a braking action directly on the axles. It 
will be understood that the hand brakes can be operated 
without putting the magnetic brake in action. Resistances 
are provided between the motors and the magnets so as 
to regulate the current in the latter. In this way mag- 
netic adhesion can be controlled at will. It is further 
claimed that an advantageous effect is produced by the 
pressure on the rails by the wheels, due to the attraction 
of the magnets. The electromagnetic brake clearly supplies 
a most important means for checking the speed of a car. 
Colonel Yorke describes it as ‘‘ one of the most modern, 
and, when properly used, one of the most effective devices 
for controlling tram-cars.”’ 
The car had been recently overhauled, and was appar- 
ently in good condition. New brake blocks had been fitted 
the clearance being 1/16th of an 
inch when off. The driver stated that one of the sanders was 
