PATKNTS. 



TI3 



the windlass. Outside tho end bearings of the 

 windlass uro the usiuil drums for ojM-rating hii^v- 

 scr- i.r other lines in heavy hauling or hostile,'. 

 Wln'ii -team is used in operate tin- windlass tho 

 connect ion is made through an endless screw OJH*- 

 ratingon the large cog wheel, wliicli is in that case 

 shaped differently to accommodate the changed 

 conditions. It is MHIIC! imes desirable to operate 

 the friction hand Iroin the lower dock, and in 

 that case the lever is placed us in Kig. liG, which 

 shows the ingenious method whereby tho wheel 

 is clasjK'd on all sides by the friction band. A 

 i>thc lever, // an eccentric bearing, C'the friction 

 band. When the lever is depressed in the direc- 

 tion of the arrow it is evident that the lower part 

 of the band is powerfully drawn toward U, and 

 any doircd pressure exerted upon about three 

 quarters of the periphery of the wheel 



Itiiuu'iilur \ ision in (jreat Telescopes. 

 Tin 1 production of the telescope represented by 

 the accompanying drawings \vas suggested by 

 the fact tliat .Nature created men with two eyes, 

 but none with one; and as the Creator never 

 makes a mistake nor wastes his energies in 

 making two things where one is sufficient, it 

 was logical to suppose that two eyes are better 

 than one for the purposes of vision, and that 

 when we peep into the telescope with om rye 

 shut we are only using half the means that Na- 

 ture has placed at our disposal in endeavoring 

 to solve the visual problems of the universe. 

 The doctrine has been persistently set forth that 

 any attempt to adjust two great telescopes into 

 the conditions of binocular vision must of ne- 

 cessity result in failure, as two such instruments 

 would always show the same object double ; but 

 the double telescope here represented showed, 

 when completed, only a single image of any ob- 

 ject at which it was directed; and when it is 

 properly adjusted to the eyes of the observer, 

 two images of the same object can not be seen, 

 but the image is better denned and more than 

 twice as bright as that in either telescope when 

 viewed with a single eye, for the reason that the 

 loss of one eye makes us more than half blind. 

 Fig. 27 is a longitudinal section through the cen- 

 ter of the instrument, showing the convergence 

 of the light of a star that enters it. In the in- 

 strument A, L is the object glass, and the dotted 

 lines C, C, represent the light being gathered to 

 the focus P, by which it may be seen that it is 

 only the ordinary form of telescope. Its com- 

 panion, B, is so placed as to be perfectly parallel 

 with A. and they are secured together by the 

 couplings D, E. The object glass in this instru- 

 ment is within the tube, but farther back than 

 that of its companion. The focal length of the 

 two object glasses being the game, it is neee-sary 

 to place it far enough back in the telescope to 

 compensate for the length of the cross adjust- 

 ment, G, at the final focus, the nature of which 

 will l>e understood by following the dotted lines 

 that converge from the object glass. (). to the fo- 

 cus. A prism or speculum at II reflects this 

 converging light transversely to its original di- 

 rection, as shown at I ; it is then intercepted at 

 J bv another prism or speculum and reflected 

 to the final focus of that telescope at K. The 

 cnxs adjustment G is constructed <. ,-i- to slide, 

 in order that the two eye-pieces F and K may lx> 

 adjusted to the different distances between the 



ere of different observer*. In thi* trlpw-on*, B, 



then- is iil~.au additional rack and pinion, I', for 

 moving lh' objict gin.-*, o, a little bit. k or for- 

 ward. HO that the eye-pieces. Fend K. may beeo- 



ilieidetlt ill (Million. The eve-pie, e K htttj tho 



direction of the dotted line .M, which i.,n\.-rp i 

 to the point N, on I he optical axis of A, suflieieiitly 

 di>tant from the observer* to gi\e the eve an 

 easy angle of 'vi-iuil 

 convergence. At thin 

 iH.ini the image* of 

 both telescope* coa- 

 le-i-e. and then-by pre- 

 sent to the observer 

 only a single image of 

 a single object, and 

 instead of seeing two 

 images of the same 

 object it is simply 

 impossible to divide 

 the single binocular 

 image into two unless 

 by pressing the ball of 

 one eye out of its nat- 

 ural position. When 

 it is necessary to use 

 this instrument for 

 two observers at the 

 same time, or by mas- 



F K 



FiQ. 27. 



ter and piinil. the cross adjustment, G, is re- 

 moved, and then the eye-piece end takes t In- 

 form shown by Fig. 28. Thus the instrument 

 is practically two telescopes, which will always 

 have the image of the same object in their re- 

 spective foci, thereby furnishing the master with 

 the means of describing to the pupil. 



One of the advantages of constructing great 

 telescopes for binocular vision is to be found in 

 the fact that the intensity of light brought to 

 the focus by two object glasses of thirty inches 

 in diameter would l>e greater than that brought 

 by a forty-inch objective to its focus. As their 

 relative focal lengths would be proportioned to 

 the diameter >I their object glasses, the obcrva- 

 tory for the shorter instrument would IK- much 

 smaller and less costly than that of the fortv- 

 inch instrument, but the double telescope would 

 have much the greater space-penetrating power. 

 As that quality is proportionate to and depend- 

 ent upon the relative brilliancy of the image at 

 the focus, the space- penet rat ing powers of the 

 double instrument would IK- su|>enor t<> that of 

 the greater in the proportion of sixteen to 



