APPENDIX. 



THE annexed Prospectus was first printed in Newcastle-on- 

 Tyne, in 1818, and afterwards in 1820, in London. From the 

 first, copies were sent to a number of gentlemen devoted to 

 science, with a view to excite inquiry. 



I had originally intended to have published a small treatise 

 by subscription, but abandoned the idea, determining to wait 

 the period when perhaps some further discoveries in physical 

 science might create an interest on the subject, which at the 

 time did not appear to prevail. 



That epoch has at length arrived ; in every new work I now 

 have the gratification to find some fact in support, or some new 

 hint or opinion advanced, which shews the correspondence of 

 the writer on one or more points, in which we perfectly coin- 

 cide in opinion, and such parallel concurrences, often from 

 particularly distinguished authorities, are most gratifying, as 

 they afford me conviction, that I am not a solitary, indulging 

 in vague and visionary fallacies, for there are hundreds who 

 think and reason as I do, on a considerable portion of what I 

 conceive it eligible to investigate, with a view if not fully, at 

 least partially, to establish. 



When this Prospectus was written, in the winter of 1817, 

 the greatest correction of the errors of the Newtonian Spectrum, 

 had been confined to Dr. Wollaston's reduction of the prismatic 

 Colours from SEVEN to FOUR. I repeated his experiments, 

 and was concluded by the same fallacious views, as in my 

 observations, I found the red and yellow rays well defined, at 

 one end of the Spectrum, the blue, and violet equally so, at the 



