TELESCOPE. 



the I'mall fpcculum. Tliis large fpeculiim is put in with 

 fome liberty, as is alfo the Iniall one in a box containing a 

 fpiral fpring atting agaiiill it to prevent tremors ; B is the 

 eye-piece of tlic Huygcnian kind, of whicli there are ufually 

 two or three, according to tlie C/.e of the inftruijient. The 

 femi-circle D is racked, and the handle H turns the fcrew 

 that gives elevation, while the handle I gives the horizontal 

 motion, by its fcrew driving the racked hurizontal plate E ; 

 both which are cleai-ly feen in the figure. The vertical 

 motion takes place at the centre of gravity of the tube at 

 the top of the frame between E and D, and the horizontal 

 motion is from an axis in the centre of the racked plate E, 

 which axis has a long bearing down a tube to G, under tiie 

 junction of the three legs. The three-barred bracing piece 

 F has a joint at each leg, and alfo at the circular brafs plate 

 in the centre, fo that a little force applied under this plate 

 will raife it, and allow the legs to come together into contaft, 

 as well as the three arms that keep the legs open when the 

 iland is ufed. This mounting is very portable and fteady, 

 particularly when the tube- is fliort, and is every way con- 

 venient for ufe, except that botli the vertical and horizontal 

 motions are flow motions, the former of which is tedious 

 when a great change of altitude is wanted in a given time, 

 but the latter is in lome meafure remedied by the portability 

 of the ftand, which may be eafily turned altogether, to face 

 any particular objcft. 



When the length of the tube is three feet .and upwards, 

 and proportionably wide, jig. 2. reprefents a ftand that is 

 greatly to be prefen-ed to that reprefented by jig. i . We 

 (hall put the fame letters of reference to the fame pails, 

 though there is a difference in the conftruftions that may 

 require explanation. This ftand was contrived and firit 

 made by Tulley, who, we underftand, claims aifo the inven- 

 tion of the three-armed brace F, in /f^. i, above defcribed. 

 The contriver has evidently contemplated all the requifites 

 for a good conftruftion, and has fucceeded in the execution 

 of his plan : A B, as before, is the main tube, B one of the 

 eye -pieces, C the adjufting fcrew for diilinft vifion, hid in 

 our drawing behind the tube ; but in place of it is feen the 

 finder, attached above the eye-end of the. main tube. At D 

 is a (liding-piece of metal with a cyhndrical hole, through 

 which the round rod H D palTes, and to which it may be 

 fixed, by the prefTmg fcrew D, in any given elevation ; to 

 this fliding-piece D, two rods D K, D K, are attached by 

 two Joints, and two other joints attach them below to the 

 fiame E K, fo that thefe rods K, K, are at liberty to rife 

 and fall as the tube is elevated or depreffed, but not until 

 the fliding-piece at D has moved along the rod H D. When 

 the piece D is fixed to the rod by the fcrew of prefTure, it 

 forms a point of bearing for the tube at a diftance from the 

 centre of motion, ^^hich is at the centre of tlie tube's oravity 

 above the frame of brafs work, feen in the figure ; thus the 

 telefcope is kept fteady by two points of bearing in every 

 degree of elevation, though thefe points will recede from 

 cai:h other gradually as the telefcope is depreiTcd towards an 

 horizontal pofition. When the fcrew at D is tnrned back, 

 the motion is fufficiently quick ; but when it is faft, the 

 flow motion is produced by the handle at H ; for while this 

 handle turns the rod, a fcrew cut on its interior end works 

 m a fixed cock, near H, tliat has a female fcrew within it, 

 and draws the fliding-piece and rod together towards the 

 eye, and thus elevate? the tube, while the joints of the rods 

 K, allow a correfponding elevation in them ; fo that, with- 

 out undomg the fcrew at D, a flow motion up or down is 

 produced by merely turning the handle H, which motion, 

 hemg free from jerks, is very pleafar.t. Between the brafs 

 »ame bearing the ttlefcope and the large wooden frame E F, 



are three circular plates, the uppermoft of which is attached 

 to the brafs frame, or may be laid to form the bafis of it, 

 and has an axis of fteel fail in its centre ; t!ie fecond circular 

 plate is racked at the concave edge all round, and has a 

 circular hole in the centre, juft large enough to receive the 

 fteel axis we have mentioned ; the third circular plate forms 

 the top of the wooden tripod, and has alfo a hole in its 

 centre, juft fufficient to admit the fteel axis above defcribed ; 

 but its diameter is fomewhat lets than the diameter of the 

 .racked plate next above it, fo that a rim, made faft to the 

 racked plate, furrounds it, in the manner of a box-lid ; but 

 there is no other faftening of thefe three plates together, 

 than the prefTure occafioned by the fuperincumbent weight 

 of the telefcope, and of its fubjacciil frame E K K : the 

 axis, or fcrew, of the handle I is made faft to the upper- 

 moft plate of the faid frame, and takes hold of the notches 

 in the racked plate below it, fo that when the telefcope ii 

 turned round in azimuth, by a quick motion, it takes the 

 frame under it, and alfo the racked circle, round along witL 

 it, while the ftand or wooden four-footed frame E F ftands 

 quiefcent ; but when the quick motion is finiflied, the handle 

 I is ftill in its place at the eye-end of the tube, and turning 

 it round, will give the requifite flow motion ; for turning the 

 handle, in conneftion with the racked plate, turns the fuper- 

 incumbent frame and telefcope, without any motion being 

 given to the racked plate itfelf, which is now kept down to 

 its place by fimple prelfure of its load above. The ftand, or 

 large wooden frame, is braced in all direftions, as may be feen 

 in the drawing, and might be advantageoufly made of call -iron, 

 as it is not contrived for the convenience of portability. 



The beft ftand for the Newtonian telefcope is that which 

 is reprefented by Jig. 3, in which A is the elevated moutli 

 of a feven-feet tube, and B the place of the'large fpeculum, 

 that reflefts the rays of light back to. the fmall diagonal 

 plane metal near C, which, by a feccnd refledlion, brings 

 them to a focus at the eye-piece below C, as feen in the 

 drawing. Above C is the finder, the upper end of which 

 has a Imall achromatic objeft-glafs, and the lower end the 

 eye-glafs. The upper end of the tube refts on a fupport D, 

 that IS capable of being raifed or lowered flowly by a pinion 

 on the axis of the handle under J), while the lower end 

 rells on the horizontal bar of the frame E F, tliat is 

 fufpended by a pulley over F ; the four pivots a, b, c, 

 and di of the faid frame, fliding in the open grooves, 

 feen near thofe letters, in the main frame, keep the fmall 

 frame in any given fituation, and allow a free motion, 

 firft down the vertical, and then down the inchned pieces, 

 that compofe the main frame, as low as to G and H ; 

 and when the lower end of the tube has been depreffed into 

 this fituation, the tube may have an elevation approaching 

 towards the zenith : for not only is the upper end eleva- 

 ted by the handles at J for the quick, and at D for 

 the flow motions ; but the lower one is depreffed by 

 the handle at I, round which the cord is coiled, that goes 

 round a fixed roller at K, and two others at L and M, 

 before it embraces the pulley N, and is hooked to a pin 

 at O, above the frame. The reft of the main frame is fo 

 clearly exliibited in the drawing, that no farther defcription 

 of it is neceffary. In fome of the inftruments of this con- 

 ftruftioji, when the handle J is omitted, and a quicker motion 

 in altitude is required; and alfo a greater elevation than can be 

 given fimply by the handle at D, the fecond fquare Hem that 

 ■ carries the pinion of the handle is raifed by hand, and kept to 

 its elevation by means 01 a fecond rack, which is fet at 

 liberty by prefTmg a button at P, conneded with the 

 fpring-catch ot the rack, when this fq^uared ftem is lowered 

 again, all which raotiens will be readily comprehended by 



any 



