COMPARISON OF CONTINENTAL AND ENGLISH MODELS 257 



Heichert, and the rest. It is a non-inclining instrument, with a 

 short tube on a narrow horseshoe foot, in which steadiness is 

 obtained by sheer weight. It has a sliding-tube as a coarse adjust- 

 ment, and a direct-acting screw for the fine adjustment. The stage 

 is small, and the aperture in it is relatively still smaller, of no service 

 in reaching the focus of an object by touch with a high power. It 

 is provided with spring clips, and a diaphragm immediately below 

 the stage, and a concave mirror. Now it has been said that the fact 

 that the Powell stand, e.g. of forty-five years ago. adapts itself without 

 material change to the most modern appliances would be looked 

 upon by the German student as being ' no commendation.' because 

 it would mean that they were more elaborate than was necessary. 

 1 nit what are the facts? Let us take an Oberhauser of 1837. ami 

 compare it in one essential particular only with a very early Powell, 

 designed in 1834. It was a stage-focussing instrument. As a fact 

 the Oberhauser will not focus a low-angled ^-inch objective properly ; 

 the fine adjustment works in jerks, and the lateral movement cau>r- 

 the object to go out of the field. The Powell will now work an 

 apochromatic of 1'4 N.A. oil immersion with accuracy and precision : 

 but if a 11 apochromatic oil immersion of 1'4 were placed on the Ober- 

 hauser it would be at great risk to the objective. Xmv even in early 

 days accurate focussing was surely a vital matter, and the foresight 

 that could anticipate what might require more delicate focussing than 

 the objectives then in use was wise, and to the student profitable. 

 The Powell No. 1 stand, as it is now. was in the main constructed in 

 1849, so far as regards tripod foot, limb, coarse adjustment, and fine 

 adjustment with Turrell stage. The alterations that have been 

 introduced have been the concentric rotary stage (1861), and the 

 present form was manufactured in 1869. 



A stih-staije condenser was rarely used, because up to a compara- 

 tively late date (1874) it was regarded by many on the Continent 

 as a mere elegant plaything ; its true value was not perceived. 



On this model all the microscopes of the firm of Zeiss. of Jena, 

 are constructed, as they are used almost exclusively on the Conti- 

 nent, and are regarded in many of the universities and medical 

 schools, both here and in America, as possessing all the qualities 

 required for the best biological research. 



If we examine the finest of these instruments made up to 1885, 

 we are impressed, as we always are, with the beauty and care of the 

 workmanship and finish of this firm ; but there is the same liea\y 

 horseshoe foot, steady enough while the instrument is non-inclining, 

 only needlessly heavy, requiring common ingenuity alone to get 

 equal steadiness with one-fourth the weight. But since this instru- 

 ment has been adapted to the English form by being made to incline 

 to any angle up to the horizontal, the foot but insecurely balances 

 the instrument, and it is not difficult, as it is not uncommon, to topple 

 it over. Indeed in their photo-micrographic outfit the Messrs. 

 Zeiss practically see this, for they supply (inntld-r foot to u-Jnch the 

 microscope is clamped. Messrs. Bausch and Lomb tell us that the 

 foot of their ' B B ' Continental microscope is //< -iic'ilij leaded to ensure 

 greater stability.' Sidle and Poalk (1880) and McLaren (1884), and 



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