Royal Astronomical Society. 531 



quire are disappointed to find that they must lower their opinion of 

 great men, and are perhaps led to do it to a greater extent than jus- 

 tice requires. Our usual popular treatises speak of Copernicus as if, 

 besides himself, he had in him no inconsiderable fraction of Kepler, 

 Galileo, Newton and Halley. What is a person to think who comes 

 from those histories to actual investigation, when he finds in Coper- 

 nicus himself the immovable centrum mundi (only reading sun for 

 earth) of the Ptolemaists, their epicycles, and a suspicion, at least, 

 of the solid orbs ? 



On the Formation and Application of Fine Metallic "Wires to 

 Optical Instruments. By Mr. Ulrich. 



Dr. WoUaston, in the Philosophical Transactions for 1813, pro- 

 posed a method of forming wires of gold or platinum of any degree 

 of tenuity. The discovery does not appear to have been much used, 

 owing, as Mr. Ulrich supposes, to the difficulty of application. 



Mr. Ulrich forms the fine wire by inserting a gold or platinum 

 wire in the centre of a silver cylinder of much larger dimensions, 

 which is afterwards drawn out by the usual process. When the 

 silver wire has been sufficiently extended, Mr. Ulrich cuts it into 

 short lengths and attaches platinS. rings to each end. The rings are 

 hooked upon a hooked fork, and the whole is plunged into heated 

 nitric acid, when the silver coating is dissolved. 



The artist may now wire his cell according to his fancy. Mr. 

 Ulrich's plan seems to be, to hold one end by an overplate ; then to 

 allow the wire to be stretched by its platina ring, and to fix the other 

 oveqjlate. He recommends using a cell of the same material as the 

 wire, as, otherwise, a difference of expansion might break or slacken 

 the w^ires. 



On the properties of Rock as a foundation of the Piers of Meridian 

 Instruments, with an Account of the Detection of a hitherto un- 

 suspected Cause of Error in the Edinburgh Transit. By Professor 

 C. P. Smyth. 



Some years ago doubts were expressed of the fitness of a rock 

 foundation for an observatory. It does not appear that any experi- 

 ments were made, or that any reason was adduced beyond this, that as 

 tremor was unfavourable to the performance of large telescopes, and 

 as rock was more capable of transmitting tremors than less compact 

 material, therefore rock was to be avoided when choosing a site for 

 an observatory. The author or authors of this opinion were pro- 

 bably but ill- acquainted with the mode of working an observatory, 

 or the requisites for obtaining accuracy in meridian observations ; 

 yet it is certain that an undue importance was attached in some cases 

 to these very idle surmises. At the present time it is not likely that 

 any intelligent person would be misled by such authorities, and it 

 is therefore unnecessary to mention here the mischief they have 

 caused *. It is to be wished that the founders of future observatories, 



* The effect of tremor on a telescope is probably familiar to every read- 

 er of tfiis notice. It causes a sort of burr round the object, and destroys 

 the sharpness of outline and definition. This is probably more injurious in 

 reflecting than in refracting telescopes ; but we may fairly doubt whether it 



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