304 



SCIENCE. 



ON PHOTOGRAPHING THE NEBULA IN 

 ORION.* 



By Professor Hexrv Draper. 



The gaseous nebulae ate 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 som; 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 bins 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 the earth's motion and 

 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 <~f 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 use:l to obtam the picture are as 

 follows: 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 mourned on an equa- 

 torial stand and driven by a clock that 1 made myself. 

 The photographic plates are gclatino-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. B 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 

 of photographs taken at various times of the 

 wiater 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* 



Propessok Henrj Morton. 



experi nents, which I made in deter- 



nrning ti tree of tl Brush dynam >- 



'iic, and va ious instruments for the 



.1 cm nl of electric currents of 



low that each pair of coils on the armature 



. i lop . a fluctuating electr >-moti\ e 



in h gives a ki id of -ova! curve 



!lll. 



h pair ol 1 oils are com- 

 tnd, that 1I1 y show a kind ol eight-lobed 



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 eqial to that from which it 

 breaks ; thus suppressing a spark, but only at a certain 

 sacrifice of theoretical efficiency. 



11 y of Sciencsi, N. V., i38o. 



APPLICATION OF THE PHOTOPHONE 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 oi the ob- 

 servatory at his disposal. The weather being very fine 

 on Saturday last (October 30), Mr. Bell cime 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 ob'.ain 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 

 imagts upon the selenium apparatus. This would be a 

 means oi 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 

 litter 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. 



LKCTURE PHOTOPHONE. 



A simple form of Pnotophone, 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 

 1 ,ondon. 



The reflector for receiving the light is discarded, and 

 the b am focussedon the selenium by the lens. 



The two lenses used cost only about six dollars, and 

 Mil is se.it fourteen feet. 



The selenium cell was made by spread ng melted se- 

 len 1 1 ' 1 1 over sheets ol mica, and then crystallized by heat. 

 For mi ca Prol II recommended microscopic 



glass. 



! was 14000 ohms in the dark 

 and 6500 in the light- Speech was distinctly transinit- 

 1 :d by this apparatus. 



