SL//i.VCE-GOSS//: 



6i 



CIIAI'TKKS |()|< VOUNi; AS TRi )N( >.Mi:US. 



Ilv I'kank C Dknnkti. 



ISE OI' THE TEI.KSCOPE. 



{Continued Jrotn p, jj). 



Is making nbs'.Tvaiions of tlie nmon, ihi; piuition of 

 tile ttrmiiiiUiir shmilil iilwiiys ho given. In other 

 words it shouhl he stated whul ohjccts are situated un 

 the boundary, hciween hri(;htness and shade. 



If it bo desire<l to observe faint objects, whether 

 neliulae, comets or mintrle points of light, do not, for a 

 long time before the observation, ex|)ose the eye toany 

 brilliant light. Professor W. K. Brooks, who has 

 discovered so many comet >, will never allow himself 

 to look at .1 brilliani light, that he may not injure the 

 sensitiveness of the retina. .Sir. J. K. VV. Ilerschel 

 u.sed to prepare his eye by remaining for a quarter of 

 an hour in a totally dark room. Never get exciterl 

 before an observatioi\, as the eye is not then In fit 

 condition to see delicate detail. In looking for faint 

 objects, if they are not at once seen, direct the eye lo 

 the edge of llie field of view ; but keep the attetition 

 in the midille, where they are suspected lo be, and 

 very often success will result. This is called using 

 averted, or oblique, vision. 



Alt hour or two after sunrise is usually the best 

 lime to observe the sirn, before the atmosphere 

 gels heated. If, however, the sun is an object 

 of study, look at it, if possible, every two or 

 three hour,-.. Close double stars are often best seen 

 on a still frosty evening with a slight fog. If the 

 observer has an equatoreal with circles, an hour before 

 sunset is a good time. .\n east wind often aftects 

 even double star observations, making the star 

 discs triangular instead of round. The breaks between 

 clouds are often better when looking for .stars in 

 daytime than an apparently clear sky. 



If telescopes of larger aperture than 6 inches are 

 being employed, definition may often lie improved by 

 using a "stop" to reduce the working diameter .some- 

 what, when the air is not good. Such stojjs should 

 be placed as near to the objective as possible. 

 Reflectors should have a door in the tube just above 

 the speculum, to permit of the in.sertion of stops, or for 

 covering the mirror. If the air is unsteady early in 

 the evening, do not give up ; a little later there may 

 be an improvement. In large towns the air generally 

 improves after midnight. It is also often very 

 transparent after rain has fallen. Karly morning is a 

 favourable time for ob.ser\ation. 



When not in use always keep the objectives 

 covered to prevent dust from settling upon them ; and 

 in the case of Newtonians cover the small speculum 

 as well. This should be done in the open air, as to 

 bring the telesci>pe into the wanner atmosphere of the 

 house would cause '" dewing." If an objective is 

 '■dewed," do not clo.se it up in that state, but bring 

 it into the warmth near, but not close to, a fire and the 

 dew will soon disappear. Do not attempt to rub a 

 silvered mirror when clamped, or it will remove the 

 film. When it is necessar)' to clean an objective first 

 remove any particles of dust with a camel's hair 

 pencil, and then clean, aided by the breath, gently 

 with a soft, even, chamois leather, or a soft silk 

 handkerchief. When not in use the lealher, -n- 

 handkerchief, should be kept in a wide-mouthed 

 stoppered bottle. For cleaning the eyepiece lenses, 

 after the dust has been removed, nothing is belter, 

 when aided by the breath, than a piece of clean 

 blotting paper rolled to a point and scraped with a 

 knife. For the lacquered hrasswork anything mote 

 than a duster will only damage the lacquer, and spoil 

 its good appearance. 



When lenses or eyepieces arc lo be screwed in, 

 always give a back turn first and the threads drop in 

 with a siuip, then screw right away ; otherwise 

 deliciile threads are often spoiled. 



An eijualoreal wilh circles re<|uires three adjust- 

 ments to gel it into proper position, after Ixring 

 approsimatelv placed. First turn the telcsco[>c, 

 whilst east of the hour circle, lo a star nearly on the 

 meridian, and take the declination rc-ading of 

 the circle. Nexl reverse the inslruinenl to 

 (he west side of the hour circle, set it on the same 

 star ami again lake the reading. Halve the difi'erence 

 between ine two reailings and alter the vernier to 

 read the mean. These double readings should be 

 taken three or four limes, until, whether the telescoije 

 is east or west of the [xilar axis, the readings of the 

 declination circle are identical. Secondly, turn the 

 telescope to any star, whose declination is known, 

 close to the meridian, and as near the zenilh.as possible. 

 Read its declination from the circle. If this does not 

 agree with its declin.ation given in the " Nautical 

 .\lmanac" rai.sc or depress the polar axis, until the 

 readings tally, by means of the screw pl.aced for that 

 purpose. Thirdly, set the telesco|)e on any known 

 star about due east, and having an altitude of about 

 45". Read its declination on the circle allowing 

 for refraction, if .accurate the polar axis of the 

 instrument is truly in the meridian. If the north 

 declination reads too great, the norlh end of the polar 

 axis is too far east and ti'ic versa. The whole 

 instrument must be moved in azimuth until the 

 readings are accurate. When these adjustments have 

 Ijeeii made, go over them all again for verification, 

 after which the advantages of the equatoreal stand 

 will be appreciated. 



.\ good inaxint to follow is that " every observation 

 not intended as a mere relaxation, should be directed lo 

 ascertain some as yet unknown fact." Do not go to 

 the instrument prepos.se.s.sed with the intention either 

 to .see, or not lo see any given object, or the 

 probability is, there will be hallucination. I'orgel- 

 fulnes,s of this is the cause of many errors. It is best 

 to go to the telescope, see as much as it will 

 show, make carefid notes of what is seen, and 

 aftersvards compare obser\-ations w ith those of others. 



It is alsvays well to wrap oneself up waimly. and lo 

 stand on a board whilst at work ; but very little notice 

 need be taken of the common prejudice against 

 " nighl air." It is a fact tha' astronomers, as a class, 

 are long-lived. 



If it is desired to have an observator}-, the cheapest, 

 and for many rca.s<)ns best, pattern to adopt, is the 

 "■ Herthon." It was first described in the " English 

 Mechanic," (Jctober 13th and 20th, 1S71, by the Rev. 

 K. L. Herthon For reflectors however, if it is de- 

 sired to use them lo the greatest possible advantage, 

 the better plan is to have a cover that can be lifted 

 right oft', or that will wheel away on rails. 



An excellent pillar to be used as a fixed stand for a 

 telescope having a pillar and claw stand can be made 

 thus : — (iet a piece of iron drain piping 4^ in. t<i 6j in. 

 in diameter, and 9 ft. long. .Sink the pipe 3 feet into 

 the ground : preferably into concrete, then fill it with 

 dry sand, 10 prevent vibration. Have three holes 

 drilled around the top end of the pipe, and have a 

 plug of wood turned .so as to fit into it. tightly. Screws 

 through the holes, will hold the plug firmly in place. 

 There is a large screw holding the claw to the pillar. 

 Get a corresponding screw made to attach to the wood 

 plug. The pillar will then screw oft" the claw foot, and 

 on to the column at pleasure. A coat of paint or 

 enamel, makes an cft'ective finish to a cheap and useful 

 erection. 



('/V i'e continued,) 



