THE writer of the article in a recent number of your journal, entitled “Note on the History of Optical Glass,” has fallen into some historical blunders and anachronisms, which are the ground of my addressing you. My grandfather was born in 1738, and would therefore have been but twenty years of age at the date when he is said to have made the acquaintance of the elder Guinand, then sixteen, in Switzerland. It is almost certain that he never was there, at any rate not as an “illustrious savant,” engaged in telescopic experiments. His sister's memoirs present a blank at this exact date, but it is evident that if he travelled at the time when he withdrew from the Hanoverian military service, it was in the character of an obscure young musician. It is just barely possible that there may be some foundation for the story now given—and if so, I should be glad to learn it—but a totally mistaken colour has been given to it by drawing on the future. What follows is still more erroneous. Dollond (the elder) was at this period at the zenith of his fame as an optician; Faraday was not born, and Herschel was an ex-bandsman; yet we are told that he “returned the following year with Dollond and Faraday.” It is probably something more than a mere coincidence that about sixty years later the son of that Herschel, the son of that Dollond, and Faraday, were associated in treating with the son of that Guinand for the glasses manufactured by the latter. Apart from this, I submit that hardly anything new is contributed in the “Note.” All, and more than all, which it contains will be found in the Biographie Universelle, under the name GUINAND, where also is mentioned the Swiss rencontre, but with the name Droz in lieu of “Herschel and Utzschneider.” According to the Biographie, Guinand was born “about 1745,” and died in 1825. It was in 1821 that the Astronomical Society was instigated to make inquiries (conducted by my father) regarding Gumand's optical glasses.