Jtn.Y, 1901.1 



KNOWLEDGE. 



105 



There arc no doubt some objections, as Cliaffers rc- 

 ni.-irks.§ to the principle of compulsory assaying and 

 marking of gold and silver wares. In this country, how- 

 ever, the svstem has existed substantially in its present 

 form since the reign of Edward I. Without speculating 

 on its origin, and while making due allowances for its 

 defects, it is est.ablished that it has resulted in tl'c 

 creation and maintenance of a high standard of excel- 

 lence for all British assayed wares, which has not only 

 raised the reputation of British workmanship at home 

 and abroad, but has also created a large amount of 

 private wealth readily convertible into n\oney l)y reason 

 of the g»larantee of value which the Hall-marks afford. 



Conducted by >r. I Cross. 



Rr-irm.RT'* Finf: Adiustmfnt (lontinned). — Since the 

 appearance of the June number, Reichert has written stating 

 that for each turn of the milled head controlling his new lever 

 form of fine adjustment, a movement of '01 m m is produced : 

 in his ordinary system of direct-acting screw, the rate of 

 movement per revolution of the milled head is -3 m m. 



It will be seen that the rate of movement is three times as slow 

 with the new fine adjustment. The new arrangement al-so permits 

 of the use of coarse screws, which are obviously not so liable 

 to wear as fine ones, and the whole of the mechanism is of steel. 



The entire construction is undoubtedly thoroughly sound 



FiG.l. — Sectional view, li.li', 

 lever arms; j, point of contact 

 with lever» controlled by screw 

 a-, b, j)oint which communi- 

 catee tlie movement from levers 

 through semi-circular connec- 

 tion c, f. 



Fig. 2. — External 

 appearance, li, h. ful- 

 crum of lever arm<. 



position that the house of Zeiss does in the optical world should 

 have devised an improvement in such an important part as the 

 fine adjustment. 



simple in design, and exceedingly 

 is a distinct improvement to tbe 



mechanically, yet very 

 efficient practically. It 

 Continental stand. 



Zeis.-'s Fine AaitT^TMENT. — This is fitted to a new stand for 

 photo-micrography and projection only, and in actual working 

 is exceedingly steady, sensitive, and soft to the touch. 



The stand to which it is applied is arranged for use with 

 Zeis-s's new Planar lenses, which work without eye-pieces, and 

 are intended for photographing large objects, there being 

 sufficient room on the stage for an object 160 mm iii diameter ; 

 and, on the other hand, it is designed to work for projection 

 or photography with objectives of the highest aperture and 

 power. 



It is extremely gratifying to find that a firm occupying the 



§ Chaffers. " Hall Marks on Plate," 8th Edit.. 1S96. p. 4.3. 



Fig. 3. — Sectional Views of Zeiss'* Improveil Fine Adjustment. 



The slowest fine adjustment they made previously gave for 

 each turn of the milled head -25 m m ; in this new one a move- 

 ment is produced of ■<)\ m/m for each revolution of the milled 

 head, that is, it is six times as slow as the ordinary pattern. 

 This in iteelf is an immense advantage. 



Fig. 4. — K, Controlling Milled Heads of Fine Adjustment. 

 (For description see t<'xt,) 



It will be noted that the two controlling screw heads are 

 parallel, and instead of being placed at the to]) of the limb, as 

 is usual in Continental models, are set ou either side of the 

 limb of the instrument. They are small in diameter, so that 

 when low powers are used they can be revolved rapidly between 

 the fingers. 



The drawings are self-explanatory. It will be seen that the 

 movement is affected by a cog-wheel system. The endless 

 screw E operates tbe cog-wheel S,, causing the long screw 51 to 

 rotate, the reactionary effect being produced by the spiral 

 spring U, 



To prevent the over-turning of the screws, a cog, S,, is 

 provided, and this travels up and down on the pin G ; stops are 

 fitted A, and A„, which come in contact with C, and C, when 



