On the Cometarium. 73 



was caused by a vacuum (of air) being made by the passage 

 of the electric fluid : but I scarcely think, had this been the 

 case, that the shilling would have adhered tor so many hours 

 as it did. I hope your readers will be induced to make ex- 

 periments for the purpose of determining the cause of the 

 adhesion, which appears to be a remarkable circumstance, 

 and worth attending to. 



I am, Sec. 

 Ma-- 7 1806. J ^ n occasional Correspondent. 



XIV. Letter from Ez. Walker, on his Instrument called 

 a Cometarium, described in our last Volume. 



To Mr. Tillock. 



SIB, Lynn, May 31, ISO.'. 



The editor of the Retrospect of Philosophical, Mechanical, 

 Chemical, and Agricultural Discoveries, after having copied 

 from your Magazine, No. 93, most part of my paper respect- 

 ing an instrument which I have called a cometarium, makes 

 the following observations : 



" This contrivance is founded upon a property of the convex 

 lens, which does not appear to be generally known : it will 

 probably furnish a representation of the figure of a comet 

 more accurate and natural in most respects than has hitherto 

 been obtained. But the name of cometarium is not very 

 appropriately applied to the instrument, since it neither ex- 

 hibits the relative magnitudes of the sun and comet, nor 

 nearly the true orbit and motion of the latter. Indeed, there 

 is reason to apprehend that the contrivance, so far from 

 serving as a cometarium in its present state, cannot even 

 be adapted successfully to any system of machinery which 

 will correctly exhibit the phenomena of the solar system." 

 — Retrospect, vol. ii. p. 20. 



The objections made by this gentleman to the name of 

 my in&trtirjoent do not appear to be well founded ; for a pla- 

 netarium i*ithcr exhibits the relative magnitudes, distances, 

 motions, no; the true figures of the orbits of the planets, and 



