: 
May 6, 1886 } 
NATORE 2i 
experience it does not sufficiently approximate to a straight line 
in the part of the curve near the origin, and gives too high 
results for large values of c. 
One purpose of the present investigation is to give an ap- 
proximately complete construction of the characteristic curve of 
a dynamo of given form from the ordinary laws of electro- 
magnetism and the known properties of iron, Let 7 be the 
number of convolutions on the magnets, c the current round 
the magnets, 4, the mean length of the lines of force in the iron 
of the armature, A, the area of section of iron in the armature, 
/, the distance from iron of armature to iron of pole pieces, A, 
the area of the magnetic field in which the wires move cor- 
rected for its extension round the edge of the pole pieces, /3 the 
total length of the magnet cores, A, the area of the magnet 
cores, 7, the mean length of lines of force in the yoke connect- 
ing the magnet limbs in machines of the type on which we have 
principally experimented, A, the area of section of the yoke, 
7, the mean length of the lines of force in each pole piece, A; 
the main area of section of pole piece, I the total induction 
through the armature when no current passes in the armature, 
and vI the total induction in the magnet cores ; and, finally, let 
the relation between the magnetic force (a) and induction (a) 
(vide Thomson, ‘‘Electrostatics and Magnetism,” p. 397, and 
Maxwell, ‘‘ Treatise on Electricity and Magnetism,” vol. ii. 
p. 24) be represented by the equation a = f(a), then the 
characteristic curve is— 
I I I ees I; 
4mnc = W(x) + 2%, ar af (i) a ute) 2s H(i), 
Ay Ay 
If the relation between a@ and a@ be given in the form of a curve, 
this formula indicates at once a perfectly simple graphical con- 
struction for the characteristic. ‘Taking the curve of magnetisa- 
tion determined by one of us for wrought iron, and constructing 
a characteristic in this way, we have obtained a theoretical curve 
which agrees over a long range with the actual results of ob- 
-Servation on a dynamo-machine more closely than any empirical 
Y 
formula with which we are acquainted. 
To determine v, a wire was taken once round the middle of 
one magnet and connected to a ballistic galvanometer, a known 
current was then either suddenly passed round the magnets or 
short-circuited, the elongation of the galvanometer being noted. 
A similar observation was made with the same current, the gal- 
vanometer being connected to a single convolution of the arma- 
ture in the plane of commutation. The ratio of the two 
elongations is the value of v. 
The distribution of the waste field (» — 1)I was roughly ascer- 
tained in a similar manner. 
The currents in the fixed coils round the magnets are not the 
only magnetising forces applied in a dynamo-machine. The 
currents in the moving coils of the armature have also their 
effect upon the resultant field. In well-constructed machines the 
effect of the latter is reduced to a minimum, but it can be by no 
means neglected. This introduces a second independent variable, 
viz. C, the current in the armature. The effect of the current 
in the armature depends upon the lead given to the brushes. 
Denote this by A, which we may also regard as an independent 
variable, as it is subject to arbitrary adjustment. 
If I = F(4mzc) be the characteristic curve when no current 
passes through the armature, then 
em Mt 
v 
il as 
4amC & ay (anne = se, 
Vv 
where 7 is the number of convolutions in the armature. Here 
we omit the comparatively unimportant portion of the magnetic 
force in the core of the armature and the pole pieces. From this 
formula it is not difficult to deduce a geometrical construction 
for the characteristic surface (vide ‘‘ Practical Applications’of 
Electricity,” lectures delivered at the Institute of Civil Engi- 
neers, 1882-83, p. 98). The equation may be thus expressed 
in words, if A be such that the coils at commutation embrace the 
whole or nearly the whole induction. The effect of the current 
in the armature upon the difference of potential between the 
brushes of any machine, is the same as that of an addition to 
the resistance of the armature proportional to the lead of the 
brushes, and to the ratio of the waste field to the total field, 
= 5 C i mr . 
combined with that of taking the main current yn times round 
the magnets in a direction opposite to the current c. Many con- 
sequences can be deduced, of which we may notice the follow- 
ing :—In a series-wound dynamo C is equal to ¢, and ife¢ be 
increased beyond a certain point, I must attain a maximum and 
then diminish ; this has been frequently observed. We now 
see that it depends upon the existence of a waste field. 
Secondly, let the coils of the magnets be entirely disconnected, 
and let A be the negative ; if the armature be short-circuited 
through a small resistance and be run at a sufficient speed, a 
large current may be produced in the armature. This latter 
deduction we have verified by direct experiment. 
The efficiency of the type of dynamo-machine upon which the 
experiments before indicated have been made, has been accu- 
rately determined by the device of coupling two similar machines, 
both mechanically and electrically, so that one should act as a 
generator of electricity, driving the other electrically, whilst the 
latter acted as a motor driving the former mechanically ; the 
loss of power required to keep the whole combination in move- 
ment being determined by direct dynamometric measurement, 
and the power passing electrically from the one machine to the 
other being measured by ordinary electrical appliances. 
The whole of the experiments were carried out at the works 
of Messrs. Mather and Platt, to whom we are indebted for the 
exceptional opportunities we have enjoyed of putting theoretical 
conclusions to the test of experiment on an engineering scale. 
Zoological Society, April 20.—Prof. W. H. Flower, 
F.R.S., President, in the chair.—Mr. O. Salvin, F.R.S., 
exhibited a living specimen of a foreign worm (Aifalium 
kewense), found in a garden in Sussex.—The Secretary read an 
extract from a letter addressed by Mr. R. A. Sterndale, F.Z.S., 
to Sir Victor Brooke, concerning a case of hybridism between 
Ovis hodgsont and O. vignet.—Mr. J. Bland Sutton, F.Z.S., 
read a paper in which he gave an account of some of the in- 
vestigations he had made during the past twelve months into the 
diseases affecting the mammals living in the Society’s Collection. 
—A communication was read from Dr, O. Finsch, C.M.Z.S., 
describing a new species of wild pig from New Guinea, which 
he proposed to call Sws miger.—Mr. Smith Woodward read a 
paper on the relations of the mandibular and hyoid arches in a 
Cretaceous shark (Aybodus dubrisiensis, Mackie).—A communi- 
cation was read from Prof. R. Collett, of Christiania, C.M.Z.S., 
containing an account of the hybrid between the willow-grouse 
(Lagopus albus) and the black grouse (7Zetrao tetrix), which 
occurs occasionally in Norway, Sweden, and Northern Russia, 
and of which the author had examined altogether thirteen speci- 
mens, most of them of the male sex.—Mr. G. A. Boulenger, 
F.Z.S., gave the description of a new Iguanoid lizard living in 
the Society’s Gardens, for which he proposed the name of 
Clenosaura erythromelas. The exact locality was unknown.—A 
second paper by Mr. Boulenger contained remarks on specimens 
of a scarce European frog (Xana arvalis) exhibited in the 
Society’s Menagerie. 
Royal Meteorological Society, April 21.—Mr. W. Ellis, 
F.R.A.S., President, in the chair.—Mr. L. J. Petre and Mr. 
G. B. Wetherall were elected Fellows of the Society.—The fol- 
lowing papers were read:—The climate of Killarney, by the 
Ven. Archdeacon Wynne, M.A., F.R.Met.Soc. The climate 
is determined partly by its geographical position, and it has the 
benefit of proximity to the south-west coast, with all the modi- 
fying influence of the GulfStream. The temperature, however, 
is locally modified, and a decided difference is found to exist 
between that of Valencia and of Killarney. The author shows 
that Killarney is colder than many other places in Ireland, and 
this he attributes to the fact that it isin a great irregular basin 
surrounded by mountain ranges for about a third, and by hilly 
ranges elevated some hundreds of feet above the lakes on most 
of the remaining two-thirds of the circle.—Note on the proba- 
bility of weather sequence, by Lieut.-Col. C. K. Brooke, 
F.R.Met.Soc.—Account of the cyclone of June 3, 1885, in the 
Arabian Sea, by Capt. M. T. Moss. The author, who was in 
command of the s.s. Zzchw/lva, while on a passage to Bombay 
had, when near Aden, the misfortune to encounter a most 
furious storm on the above date. This storm, which was 
apparently not of very large dimensions, was exceedingly severe, 
and was accompanied by an immense wave which caused several 
fine steamers to founder.—Results of solar radiation obser- 
vations in the neighbourhood of Birmingham, 1874-84, by 
Rupert T. Smith, F.R.Met.Soc.—Results of meteorological 
ohservations made in the Malay Native State of Selangor 
during 1884, by A. W. Sinclair, L.R.C.P. These observa- 
tions were taken at four stations, viz. Kwala Lumpor, Klang, 
Kajang, and Kwala Langat. The mean temperature of the 
district is about 80°, and the rainfall about 90 inches. 
