177 



XXXVI. DESCRIPTION OF MESSRS. POWELL AND LEALAND's* NEWLY- 

 CONSTRUCTED ACHROMATIC MICROSCOPE. 



THE daily acknowledged advantages arising to every branch of Natural 

 Science from the use of the microscope, have induced us to present, 

 after some years' experience, an instrument modified to the present im- 

 provements, and more within the reach of scientific observers, than 

 that we have of late constructed, a full account of which, and figures of 

 the one made for the Microscopical Society of London, will be given in 

 a future number of this Journal. 



In the following description almost every portion of the instrument 

 is alluded to, and figures of the different parts appended ; and it has 

 been our object to give every individual credit for his improvements, 

 where at least we consider them of such importance as to be placed on 

 record. 



The points most deserving of attention are the following : The 

 double pillar, as first made by Mr. George Jackson, which possesses 

 the advantage of being lighter, and distributes the weight more equally 

 upon the foot. We have also introduced a circular motion to turn 

 the body off the stage to examine the object, and to change the object- 

 glass to prevent it from falling upon the object. The stage is made 

 larger and stronger than in former microscopes of this size, and the 

 pinion and screw are of the same diameter as in the larger instrument, 

 above alluded to. This description of stage was first constructed by 

 Mr. Turrell. There are, however, two or three other improvements 

 and modifications, such as the method for adjusting the object-glass 

 to compensate for the thickness of the glass covering the object, &c., 

 which will be found in the description of the Society's microscope. 



FIG. 1. The Microscope in the position for general use. The figure 

 forms the frontispiece of this volume. As the most convenient method 

 of using the instrument is in this position, it will be necessary after 

 taking it out of the case, to turn it by means of the pillars on its 



*Mr. Lealand, Mr. Powell's brother-in-law, has for some years been engaged with 

 him in the object-glass and optical department, and is now publicly a partner with 

 Mr. Powell. Editor. 



VOL. I. N 



