Mr Pritcliartrs Single Lem Microscopes. '527 



the cosine of 2J° to unity, the intensity of the weakest gradually 

 diminishing to zero for the rays between the red and the violet, 

 then we can calculate, with mathematical precision, all the 

 phenomena of doul)le refraction and polarisation exhibited by 

 Glauberite. 



The structure of Apophyllite and Glauberite, therefore, fur- 

 nish vf& with two unequivocal examples of minerals where the 

 real axes of double refraction are not pointed out by observa- 

 tion. Their crystallographic structure does not indicate.^ with, 

 any certainty, the locality of the axes which we l^aye now in^ 

 ferred from the laws of double refraction ; but we have no 

 doubt that the results of crystallography and optical structure 

 will ultimately coincide, when our knowledge of the primitive 

 and secondary forms of minerals shall have attained a higher 

 degree of perfection. 



Art. XXI. — Account of' the Single Lens Microscopes of' Sap- 

 phire and Diamond, executed by Mr A, Fritchard, Opti- 

 cian, London. 



Although very successful attempts have been recently made 

 in foreign countries to improve the microscope, particularly by 

 Professor Amici of Modena, yet, notwithstanding %he absolute 

 discouragement of every species of science, whether theoretical 

 or practical, this invaluable instrument has, in this country, 

 undergone the most important improvements. For this great 

 step in practical optics, England has been mainly indebted to 

 the unwearied exertions of Dr Goring and Mr Pritchard. 



With a liberality which nothing but the most ardent love of 

 science would have prompted, and which was fortunately di- 

 rected by optical knowledge, Dr Goring devoted his time and 

 his fortune to the improvement of the microscope in all its 

 forms. He was not content with speculative suggestions and 

 improvements. He submitted every idea to the test of direct 

 , experiment, and was thus enabled to give to his contrivances 

 that practical value, which is so often wanting in the inventions of 

 theoretical men. We hope to be able to lay before our readers 

 some account of the successive labours of Dr Goring, in tlie 

 New Series of this Journal, which commences with the next 



