Optics, 181 



Art. XXIL—SCIENTIFIC INTELLIGENCE. 

 I. NATURAL PHILOSOPHY. 



OPTICS. 



1. Mr Faraday's Experiments on Flint-Glass for Achromatic Experi-^ 

 inents. — A paper by Mr Faraday was read at the Royal Society on the 19th 

 November, giving a short account of the experiments made at theexpence 

 of government to obtain more perfect glass for optical instruments. The 

 paper commenced by stating, that, although glass had been brought to 

 ample perfection for domestic purposes, yet for optical instruments it 

 was far from being perfect. This fact was too well-known ; and it was a 

 singular circumstance, that the first telescope maker (Mr Dollond) had 

 not been able to obtain a perfect disc of the circumference of four and a- 

 half inches for an achromatic telescope in the last five years, nor one of 

 five and a-half inches in the last ten years. The want of an improved 

 glass for optical instruments was so much felt, that, in 1825, a committee 

 was appointed to make experiments, in order to ascertain if an improvement 

 could be made. Flis majesty's government afterwards ordered every 

 facihty to be given, and stated, that the expence incurred in the experi- 

 ments should be paid out of the treasury. A furnace had been erected in 

 the Falcon Glass Works, and subsequently one at the Royal Institution, 

 where the experiments had been carried on with the greatest assiduity. 

 The paper now read was intended as a summary of these proceedings. 

 The experiments gone into were briefly glanced at, and discoveries had 

 been made which had brought the manufacture of glass for optical pur- 

 poses to nearly a perfect state, the faults so long complained of, viz. of the 

 glass being wavy, reely, &c. being remedied to a great extent. The most 

 perfect homogeneous glass obtained by these experiments was found to act 

 perfectly. The paper went into minor details. The experiments are still 

 going on. 



2. Two Large French Achromatic Object-Glasses purchased by Mr 

 South. — At a meeting of the Astronomical Society, held on the 13th No- 

 vember, the President (Mr South) announced that he had succeeded in 

 purchasing two of the largest object-glasses tliat had ever been made. 

 One of them is nearly twelve inches in diameter, the other is above thir- 

 teen inches. The first of these object-glasses was mounted as a telescope 

 at the Royal Observatory at Paris, and the French government had ex- 

 pended L. 500 Sterling in the purchase of a stand for it, so colossal are its 

 dimensions ; but they were too parsimonious to purchase the object-glass 

 itself, which belonged to the opticians who made it. A private individual, 

 therefore, has in the meantime stepped in and run away with the prize, 

 which the French government affirmed they could not afford to pay for; 

 and it is now about to be set up in Mr South's Observatory at Kensington. 

 Mr South paid a just tribute of respect to our government, (and particu- 

 larly to the Duke of Wellington,) who afforded him every facility for 

 bringing these object-glasses into the country, not only free from exaraina, 

 tion at the Custom House, but also free from all duty. 



