32 



KNOWLEDGE. 



[February, 1902. 



ness, and tlie strain it will carry. There arc two seasons 

 for the production, namely, in spring, when the best 

 gilt is produced, and in autumn, when the quality is 

 inferior. There is an important market for this 

 speciality, and the whole production is exported to 

 Northern Italy and abroad at the average price of 

 one hundred and fifty lire per kilo. The gut is of vei-y 

 small specific gravity, so that a great deal of it goes to a 

 kilo. The cost of production is also considerable, since 

 the silk-worms must be bought just at the moment when 

 they are coming into profit for making silk, that is to say, 

 when they are at their dearest. Again, the results 

 ai-e frequently disappointing, many of the catei-pillars 

 being found, on dissection, unsuitable, so that they have 

 to be rejected. 



• ♦ — 



THE USE OF HAND TELESCOPES IN 

 ASTRONOMY. 



By Cecil Jackson. 

 My object in writing these papers is to demonstrate the 

 usefulness of hand telescopes even for astronomical work. 

 Quite small pocket telescopes will do much interesting 

 work ; they are to the astronomical observer what the 

 hand magnifier is to the microscopist. The instrument 

 should, however, magnify not less than about ten 

 diameters. 



With such an instrument all the principal craters in 

 the moon may be seen. The sunspots can also be 

 observed, if cai-e bo taken to protect the eye from injury 

 by using a dark glass. Should no dark glass be used, 

 the sun must only be observed when largely obscured 

 by fog. The disc of the planet Jupiter can be seen with 

 a pocket telescope. 



For the observing of planets it is sometimes desirable 

 to remove one of the four lenses of the eye-piece. The 

 lens next but one to the eye-end of the telescope is 

 the one to be removed. The instrument is then to be 

 used with the other lenses in their usual positions. 

 After the removal of the lens, the magnifying power of 

 the telescope will be found to be considerably increased, 

 but only the centre of the now restricted field of view 

 will be available for distinct vision. 



A good way of holding a small glass is to grasp it 

 between the fingers of either hand like a penholder, 

 and then to rest the hand on some upright support.. 

 Steady yourself with the other hand after adjusting the 

 telescope to your eyesight. In adjusting the eye-end 

 for clear vision, do not push the draw-tube straight in, 

 but twist it with a spiral motion. A very good way 

 of holding a telescope quite steadily is to aiTange the 

 two sashes of a window, one just "so much above the 

 other that the telescope, when resting on them, is in- 

 clined at the proper angle for viewing any object you 

 may wish to look at through the open^wiudow. 

 I.— THE MOON. 



I shall suppose the observer to -commence with the 

 moon, and I shall now describe some of the objects 

 visible on its surfa.co, with the help of a three-draw 

 telescope having a l|-incli object glass and a magnifying 

 power of from 25 to 35 diameters. A goodl.l-inch 

 telescope will bear a power of about 60 diameters", and 

 a 2-incli land telescope a power of about 80 diameters. 



Fig. 1 shows the moon when 3] days old at about 

 8h. 12m. p.m., June 27, 1892. 



The largest craters shown in this sketch can, however, 

 be seen with a smaller telescope if looked for closely' 

 and the glass fixed or held quite steadily. A "is 

 Langi-enus; B, Vendelinus; C, Petavius; D, E, moun- 



tains on the north and south boundaries of the Sea of 

 Conllicts (Mare Crisium). These mountains may be seen 

 as two lines of light projecting beyond the crescent 

 moon. 



Fig. 2 represents the moon at about 4h. 8m. p.m., 

 Jan. 12, 1894. Moon's age, about 5d. 13h. 



A — Thcophilus, Cyrillus, and Catharine. This fine 

 group of craters may bo well seen with a H-inch 

 telescope having a magnifying power of 25 or 30 

 diameters. Cyrillus and Catharine are connected by a 

 striking valley; while Theophilus intrudes on Cyrillus 

 on its north-west side. The western limb of the moon 

 is the right-hand one as seen in a non-inverting 

 telescope. B is a fine group of interlacing craters; the 

 largest of which is called Janssen. This is a very 



Fig. 1. Fio. 2. Fio. 3. 



striking group when the moon is from four to five days 

 old. In the late summer, or early autumn, these 

 formations should be viewed when the moon is waning, 

 about three or four days after full moon. The waxing 

 moon is best seen from January to June, and the waning 

 moon from June to December. C, Piccolomini ; D, 

 Altai Mountains; E, Sea of Nectar; F, Sea of Fertility; 

 G, Sea of Conflicts ; H, Sea of Tranquillity ; I, Sea of 

 Serenity. In the telescope, the " Seas " appear as vast 

 plains. The boundary line between light and darkness 

 ceases to be jagged where it crosses any one of these 

 plains, thus proving that the lunar surface is com- 

 paratively level here. 



Fig. 3 represents the moon as seen at about 

 8h. 20m. p.m., May 15, 1894. Moon's age, about 

 10| days. 



A, Plato. This is a fine crater, of which the floor 

 dai-kens towards full moon. Any good pocket telescope 

 will show it. B, Lunar Apemiines. This fine range of 

 mountains presents a grand spectacle at about the time 

 of First Quartor in the waxing moon, or about the 

 beginning of the Last Quarter in the waning moon, 

 when it may be seen as a line of light apparently pro- 

 jecting from the half moon into the sky. C, Eratos- 

 thenes. D, Copernicus, a splendid crater, and the centre 

 of a streak-system in the full moon. E, F, G, H, I, 

 Seas of Serenity, Tranquillity, Conflicts, Fertility, 

 Nectar respectively. J is Clavius, a magnificent crater 

 presenting a striking spectacle in an instrument magni- 

 fying 30 diameters, which will show it to have two 

 craters on its floor, as well as two others adjoining 

 its wall. The diameter of this object is 142 miles. 

 K is Tycho, which is the centre of a wondei-ful streak- 

 S3'stem. which can be well seen with a small telescope. 

 Olio streak runs across the Sea of Serenity, E. Tycho 

 itself is 54 miles in diameter, and has a central hill, 

 well seen with a power of about 30 diameters. 



