Ol'servalioiia on Ihe Ocii/nr Micromrfcr. 4U.") 



the King's private observatory in Kow (lardeiis, l>r()!if;lit tliein 

 back through Richmond Park, and then gave liieni such !i 

 dinner as the season would nfford, and invited eight eminent 

 artists and chemists from London oti |)urj)oso to meet them. 

 It strikes me, however, tliat these .v,'/;.'ortj; might have recollected 

 the party to which they were introduced, anil the site of the 

 Olservatury near the £;ate of ll!c!inu)nd Park, where tlicv dined, 

 if they conld not recollect the hospitality they experienced, and 

 the instnnneius they professed to admire. 



"Bnt the English artists," says Mr. A. in his postscript, "have 

 fahown their ignorance in making the prisms of donhle refraction, 

 o»' they would not have made them to a thickness of ten millinit;- 

 itres, instead of one,tlierel)y rendering them useless." Tiiis remark, 

 coming from talents of the fnst eminence, would have struck at 

 the root of English ingenuity, if it could have ijeen brought fairly to 

 bear on its marked ol»ject; but unfortunately for the writer, those 

 very priims of Dr. Slawinski's eve-piece, which are made the 

 butt of his eenstne, were made not only i>i. Parh, but by his own 

 optician Salcil! To which may be added, that this ocular ?Hi- 

 cromeler, which is stated to he rxactf.i/ siiriiliir (^exactcment sent- 

 liable) to those made by Fortln, is not only different from the one 

 I contrived and superintended in Paris, but contains two instru- 

 ments in one, e<|ually good, viz. an instrun)ent for measuring small 

 gles, resembling in many respects Eortin's ; aiui also an instru- 

 ment for determining by a graduated circle, and without adven- 

 titious light, the position of any line joining two stars, as it re- 

 lates to the prime vertical ; which iieic property has not yet been 

 described, and I merely mention it /lere, to prevent Mr. Arago 

 from claiming it as a French invention, in case be has made him- 

 self ae(p)ainted with the concealed spider's line which it contains, 

 and which is visible only in one position wf the two lenses that 

 constitute the eve-piece. 



When I mention two lenses only, as constituting this eye- 

 piece, the Editor of the Edinburgh Philosopliical .lonrnal, who 

 attrii<uled the inventitni thereof to Dr. Brewster, will perceive 

 that he has laboured under a mistake, in supposing that /bar 

 lenses were employed. It is a curious fact, that both Mr. Arago 

 and Dr. lirewster have separately, and at the \a>ne tunc, laid 

 claim to the invention of my eye-piece with variable powers, 

 though neither of them has yet explained the method by which 

 I constructed it. 



I have onlv fnrtbcr to remark, that .Mr.Aiago, in order to 

 convince his friends that Z/^- superintended the consiruclion of the 

 eye-piece made by.Soleil, notwithstanding it differed from bis made 

 by Kortin, has said in a note at the Ixittom ol'page '!."{(), " If I 

 Jjavc a good nicniory, in the iu'atiinncul that Nolcil hath furnislicl 



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