46 PRACTICAL TREATISE ON THE MICROSCOPE. 



great and valuable improvements in the instrument will con- 

 tinue to aid and assist the scientific world, by aiming at and 

 achieving a still further degree of perfection." 



The great advances which have been made in microscopic 

 science within the last few years, and the immense number of 

 valuable contributions to animal and vegetable physiology 

 alone, with which the scientific journals of this and other 

 countries are more or less filled, all tend to show with what 

 rapid strides accurate knowledge is being advanced; and the 

 great demand for achromatic microscopes has been such, that 

 since the year 1836, in this metropolis alone, upwards of 1000 

 first-rate instruments have been manufactured by our three 

 great makers, Messrs. Powell, Ross, and Smith, to whom 

 with Mr. Lister should be awarded no small share of the 

 honour reaped by those who, through their instrumentahty, 

 have successfully laboured in the field of microscopic investi- 

 gation. 



