304 
SCIENCE 
ON PHOTOGRAPHING THE NEBULA IN 
ORION* • 
By Professor Henry Draper. 
The gaseous nebulae are bodies of interest because 
they may be regarded as representing an early stage in 
the genesis of stellar or solar systems. Matter appears 
to exist in them in a simple form, as indicated. by their 
simple spectrum of three or four lines. It is desirable, 
therefore, to ascertain what changes occur in the 
nebulae, and determine, if possible, the laws regulating 
their internal movements. Drawings by hand have been 
made of some of the nebulae, and especially of the 
nebula in Orion, for upwards of 200 years. But draw- 
ings are open to the objection that fancy or bias may 
distort the picture, and it is therefore difficult to depend 
on the result, and to compare the drawing of one man 
with that of another. To apply photography to depict- 
ing the nebulae is difficult, because these bodies are very 
faint, and, of course, owing to Ihe earth’s motion aud 
other causes they seem not to be at rest. They require a 
large telescope of special construction, and it must be 
driven by clock-work with the greatest precision. All 
such difficulties as those arising from refraction, flexure 
of the telescope tube, slip of loose bearings, atmospheric 
tremor, wind, irregularities cf clock-work, foggy or yel- 
low state of the air, have to be encountered. The photo- 
graphic exposure needed is nearly an hour, and a slip or 
movement of a very small fraction of an inch is easily 
seen in the photograph when it is subjected to a magni- 
fier. 
The means I have used to obtain the picture are as 
follow's : A triple achromatic objective of 11 inches 
aperture made by Clark & Sons, according to the plan 
of Mr. Rutherford, for correcting the rays especially for 
photography. This telescope is mounted on an equa- 
torial stand’and driven by a clock that I made myself. 
The photographic plates are gelatino-bromide, and are 
about eight times as sensitive as the wet collodion for- 
merly employed. 
As to the picture itself the nebula is very distinct in 
its bright portions. The stars of the Trapezium and 
some others are so greatly over exposed that under the 
magnifying power employed they assume a large size, 
partly from atmospheric tremor and partly from other 
causes. It is probable that much more of the nebula 
will be obtained in pictures taken in the clear winter 
weather. This photograph was made at the end of 
September when there was some fog in the air ; but 
nevertheless, the original shows traces of the outlying 
streamers seen in the drawings of other observers. A 
series of photographs taken at various times of the 
winter season and in different years will give us the 
means of determining with some precision what changes, 
if any, are taking place in this body. 
ELECTRO-MOTIVE FORCE OF THE BRUSH 
DYNAMO-ELECTRIC MACHINE* 
Professor Henry Morton. 
Some recent experiments, which 1 made in deter- 
mining the electro-motive force of the Brush dynamo- 
-electnc machine, and various instruments for the 
accurate measurement of electric currents of great 
strength, show that each pair of coils on the armature 
of the machine develops a fluctuating electro-motive 
force, the projection of which gives a kind of oval curve 
around the centre of a diagram. 
When these curves for each pair of coils are com- 
bined, it is found, that they show a kind cf eight-lobed 
* Read before the National Academy of Sciences, N. Y., i38o. 
figure with intersecting lines in certain places. These 
intersections, if compared with the positions of the 
commutator, are found to coincide exactly with the 
points at which rupture of circuit occurs, and thus 
show that each pair of coils is thrown out, not at the 
point where its force is least, but at that at which its 
electro-motive force is equal to that from which it 
breaks ; thus suppressing a spark, but only at a certain 
sacrifice of theoretical efficiency. 
APPLICATION OF THE P 1 IOTOPHONE TO THE 
STUDY OF THE NOISES TAKING PLACE 
ON THE SURFACE OF THE SUN. 
On visiting the Observa'ory of Meudon, at the invita- 
tion of M. Janssen, Mr. Graham Bell examined with 
much care the large photographs which are being made 
there for the study of the solar surface. M. Janssen hav- 
ing informed him that he detected movements of a prodigi- 
ous rapidity in the photospheric matter, Mr. Bell had the 
idea of employing the photophone for the reproduction 
of the sounds which these movements must necessarily 
produce on the surface of the sun. M. Janssen approved 
of the idea, and requested Mr. Bell to attempt its realiza- 
tion at Meudon, placing all the instruments of the ob- 
servatory at his disposal. The weather being very fine 
on Saturday last (October 30), Mr. Belt came to Meudon 
to attempt the experiment. A large solar image of 0.65 
metre in diameter was examined with the selenium cyl- 
inder. The phenomena were not sufficiently decided to 
be regarded as successful, but Mr. Bell does not despair 
of succeeding on further examination. M. Janssen sug- 
gested that the chance of success would be much greater 
if in place of d rectly interrogating the solar image where 
the variations are produced, though responding to con- 
siderable changes on the sun’s surface, are not sufficiently 
rapid even in the most powerful instruments to cause the 
production of sounds in the photophone, a series of solar 
photographs of one and the same spot, taken at sufficient 
intervals to obtain well-marked variations in the con- 
dition of the spot, might be passed with a suitable rapid- 
ity before an object glass, which would give conjugated 
images upon the selenium apparatus. This would be a 
means ot condensing into a time as brief as could be de- 
sired the variations which in solar images are much too 
slow to give rise to a sound. M. Janssen has placed 
himself at Mr. Bell’s disposal to provide him with solar 
photographs suitable for carrying out this idea, and the 
latter has sent M. Janssen the photophonic apparatus 
requisite. It has appeared to M. Janssen that the idea 
of reproducing on earth the sounds caused by great phe- 
nomena on the surface of the sun was so important that 
the author’s priority should beat once secured. 
LECTURE PHOTOPHONE. 
A simple form of Photophone, which is sufficient to 
show the principle of the instrument, and may be used 
for lecture purposes, has been arranged by Mr. Shelford 
Bidwell, and exhibited before the Physical Society of 
London. 
The reflector for receiving the light is discarded, and 
the beam foeussed on the selenium by the lens. 
The two lenses used cost only about six dollars, and 
the beam is sent fourteen feet. 
The selenium cell was made by spread ng melted se- 
len : um over sheets of mica, and then crystallized by heat. 
For mica Professor Bell recommended microscopic 
glass. 
The resistance of the cell was 14000 ohms in the dark 
and 6500 in the light. Speech was distinctly transmit- 
ted by this apparatus. 
