104 THE MICROSCOPE 



The Standard London Microscope with Circular 

 Rotating Centring Stage 



This instrument is made in four forms. No. 3214 has a screw 

 focussing substage and is the same as No. 3211, page 98, with 

 the addition of the circular rotating and centring stage. 



No. 3215 has a rack and pinion focussing and centring sub- 

 stage and is the same as No. 3213, page 99, with the addition 

 of the circular rotating and centring stage. 



No. 3216 is the same as No. 3215, but with a large 2-inch 

 body instead of the standard size. Both the nosepiece and the 

 drawtube end of the body can be unscrewed, and a photographic 

 lens can be slid into the centre of the tube for photographing 

 large specimens. The large size body does not cut off the angle 

 of view given by such a photographic lens. Also, if the drawtube 

 end of the tube be unscrewed and the nosepiece left in position, 

 low- power lenses with a large angle of view may be used in the 

 nosepiece for a similar purpose. 



No. 3217 is the same as No. 3216, but with a rack and 

 pinion adjustment to the drawtube, and is provided with a 

 second drawtube, enabling the length of the tube to be varied 

 from 140 mm. to 250 mm. The drawtube is very large in diameter, 

 and can be provided with extra large eyepieces, 1*41 inch diameter, 

 of the No. 1 R.M.S. standard size. 



The circular mechanical stage illustrated on page 52 fits 

 any of these four models. 



This microscope, with an interchangeable binocular body 

 described later, makes a very perfect research microscope. 



The Massive Model Microscope 



No. 3201. There are certain cases in which most small microscopes give 



dissatisfaction for very delicate work, and this model was first 

 made for The National Institute for Medical Research, who gave 

 valuable assistance in the design and construction. It is intended 

 for those who feel the want of a very perfect instrument. It has 

 been made throughout on a very heavy and stiS design. It does 

 not stand much higher than the standard model, but it is unusually 

 strong and stiff, so that no vibration or flexure can take place. 

 The limb consists of a massive brass casting which extends in 

 one piece from the body to the mirror. The tail-piece and fine 

 adjustment slide are planed out in one continuous cut so as to 

 ensure the perfect alignment of the substage with the focussing 

 adjustment. The stage, which is strengthened below by side 

 ribs, is rigidly fixed on to the limb, so that it is as strong as a solid 

 piece. It is of great advantage to have a stage so solid that it 

 does not show movement under the highest powers by the weight 



