PHILOSOPHICAL TRANSACTIONS 
I. The Bakerian Lecture. — On the manufacture of Glass for optical purposes. 
By Michael Faraday, Esq. F.R.S. 8$c. 
Read November 19, December 3 and 10, 1829. 
Introduction. 
Perfect as is the manufacture of glass for all ordinary purposes, and 
extensive the scale upon which its production is carried on, yet there is scarcely 
any artificial substance in which it is so difficult to unite what is required to 
satisfy the wants of science. Its general transparency, hardness, unchangeable 
nature, and varied refractive and dispersive powers, render glass a most important 
agent in the hands of the philosopher engaged in investigating the nature and 
properties of light ; but when he desires to apply it, according to the laws he 
has discovered, in the construction of perfect instruments, and especially of the 
achromatic telescope, it is found liable to certain imperfections, not essentially 
existing, but almost always involved during its preparation, and fatal to its use. 
These are so important and so difficult to avoid, that science is frequently 
stopped in her progress by them ; a fact fully proved by the circumstance that 
Mr. Dollond, one of our first opticians, has not been able to obtain a disc of 
flint glass four inches and a half in diameter, fit for a telescope, within the last 
five years, or a similar disc of five inches in diameter within the last ten years. 
It must be well known to the scientific world, that these difficulties have in- 
duced some persons to labour hard and earnestly for years together, in hopes of 
surmounting them. Guinand was one of these : his means were small, but he 
deserves the more honour for his perseverance and his success. He com- 
menced the investigation about the year 1784, and died engaged in it in the 
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