May 1, 1894.] 



KNOWLEDGE 



101 



tbat nine-tenths of the work required to be done can be 



commanded by this instrument, it is clearly better to 

 design it to do that nine- tenths well than to strain it into 



motion in right ascension, one for the setting in declination, 

 and the fourth instead of the usual clock for following the 



stars. 



Fig. 3. — Porsjiective view male from the model of tlie proposed lustrumeut. It shows the movabh' g.iUerv to which tlie steps are attached, 



by means of whieh the observerobtains ready access to the eye end. 



doing another five degrees that would only be useful on 

 very rare occasions. 



Third — It may be urged that the friction of the water 

 will prevent the rapid setting of the instrument. 



In a telescope of this size all the motions would be 

 effected by motors of some description, guided by the 

 observer from a commutator board at the eye end, and 

 there would be no difficulty in setting the telescope quite 

 as quickly as could be expected considering its great size. 



Fom'th — It may be objected that currents will be set up 

 in the water by the moving of the telescope, which currents 

 will affect the steadiness. 



No doubt this will be the case to some extent, but 

 these will quickly subside, and the motion necessary for 

 following the stars will be so slow that no perceptible 

 effect of this kind will be felt from it. 



I would make all the motions of the telescope and 

 observing stage by electro-motors, controlled from a commu- 

 tator board at the eye end of the telescope. A one-horse 

 power gas engine would give all the power required to work 

 this telescope. This could be fixed some distance from the 

 telescope so as to avoid vibration. During observations it 

 would be used to work the air pump, which would be either 

 some form of fan such as the Blackman, or some blower 

 like Root's or Beak's. During the day the gas engine 

 would be used to charge storage cells for the motors, of 

 which four would be required, all of them being under the 

 control of the observer at the eye end. One motor would 

 be required for the observing stage, one for the quick 



STREAMS OF STARS IN THE MILKY WAY. 



By A. C. Eaky.^jid. 



I AM indebted to Dr. Max 'Wolf, of Heidelberg, for the 

 beautiful photograph which accompanies this note. 

 It represents a very rich region of the Milky Way to 

 the north of Sagittarius, and lies on the edge of the 

 great dark rift which divides the Milky Way into 

 two streams through about half its circiut round the 

 heavens. The region photographed is not very far 

 removed from the part of the Milky Way on the borders of 

 the constellation Hercules, towards which the sun is 

 drifting in space, certainly at the rate of ten mQes a second. 

 At such a pace, if the sun continues his course in a straight 

 line and his motion is not disturbed by the attraction of 

 some enormous mass of matter of whose existence we are 

 at present ignorant, it will in the course of eighty thousand 

 years have passed over a space equal to the distance 

 separating us from a Centauri, our nearest neighbour 

 amongst the stars. In a million years the sun will have 

 passed over twelve and a half times that distance, and if this 

 region of the Milky Way is twelve and a half times as dis- 

 tant as a Centauri, the larger stars shown in this photograph 

 must be very large or very bright compared with our own 

 sun. 



The plate has been etched so as to show numerous 

 streams of very faint stars whose images are not as dense 

 and black as the images of the larger stars, and in bringing 

 out these very faint objects it has been impossible to avoid 



