John L. Gillerland, late of the Brooklyn Glass-Works, is remarkably skilful in mixing metal. He has succeeded in producing the most brilliant glass of refractory power, which is so difficult to obtain. A gold medal was awarded his glass, in face of European competition, at the Great International Exhibition in London, 1852. In making rich glass, the gaffer or foreman must understand the science of chemistry sufficiently well to mix and purify his materials in the best possible manner, removing all crude or foreign matter, and combining the proper substances into a homogeneous mass. Without this practical experience and knowledge, his glass, instead of being clear and brilliant, and of uniform color, will be dull, and of many hues or shades. It is important also that his personal character be such as to command the respect of the workmen.
LENSES.
Optical glasses have engaged the attention and investigation of scientific men for centuries. We read of the wonderful exploits of the burning lens of Archimedes, and find the remains of lenses thousands of years old in the ruins of Nineveh, Babylon, and Pompeii. They are of the utmost importance in the science of astronomy. The slow progress made in perfecting them shows the inherent difficulties that exist in obtaining glass of the required purity. One of these is the different specific gravities of the material used. Hence the lower part of a pot of melted glass is of greater specific gravity than the top, causing a tendency to cords or threads, an evil which science has yet to learn to overcome. Not even the large bounty offered by the English Government and the Board of Longitude has been successful in effecting any important improvement in this branch of manufacture. Munich enjoys the reputation of producing the best lenses, and consequently the finest telescopes. Sir Isaac Newton, Gregory, Dolland, Keir, and others adopted lenses made from flint- and from crown-glass, it being necessary to use both in the construction of achromatic telescopes, one possessing as small and the other as great dispersive powers relative to the mean refractive powers as can be procured. But the inherent defect of the lenses still remained. M. Macquer remarks, "The correction of this fault appears therefore to be very difficult." He had tried in vain to remove it by very long fusion and fierce fire. Others have found this by experience not to correct, but to augment the evil. Mr. Keir is of opinion that some new composition must be discovered, which, along with a sufficient refractive power, shall possess a greater uniformity of texture.
Since then, it is certain some improvement has been made in the composition for lenses. In an English paper we find the following:—"One of the most remarkable optical lenses of modern manufacture is that produced by Messrs. Chance, English manufacturers, being an attempt by them to improve the manufacture of glass for optical purposes. The diameter is twenty-nine inches, and it is two inches and a quarter thick. It is really not a lens, but a plain disk intended for a lens, should its quality be sufficiently fine. The weight is about two hundred pounds. This piece of glass was inspected, on its first public exhibition, by eminent scientific judges. It was by them examined edgewise, transversely, and obliquely; it was viewed by daylight and by candle-light; it was tested by the polariscope and by other means; and after having been thus subjected to a severe ordeal, it was pronounced to be the largest and finest known specimen of the kind."
The promise held out by the foregoing we fear has failed, as in very many previous cases, or the world ere this time would have heard of its success. An achromatic object-glass for telescopes consists of at least two lenses, the one made of flint-glass, and the other of crown-glass. The former, possessing least power of dispersing the colored rays relative to its mean refractive power, must be of greater value than the latter. It is upon this principle that the achromatism of the image is produced, the different colored rays being united into one focus. Flint-glass, to be fit for this delicate purpose, must be perfectly homogeneous, of uniform density throughout its substance, and free from wavy veins or cords.
From the foregoing, the reader will see that, as has been said, the chief difficulty which exists in making telescopic lenses arises from want of pure glass. Every attempt to correct this evil has failed; it is well known our best telescopes and like optical instruments have always achromatic lenses, and for photographic purposes achromatic lenses are indispensable. If philosophers and astronomers have with so imperfect lenses attained so much, what may not the astronomer look for when science gives him lenses made from pure glass? If the heavens, by imperfect instruments, have so far been unveiled, to what extent may he not then be able to penetrate the pure ether, and reveal planets and heavenly bodies as yet unknown?
We close our reminiscences of Glass and its manufacture, by presenting to our readers a view of an American model glass factory of the present day.[4] By comparing this view with the sketches heretofore given of the early Venetian and French factories, they will perceive the very great improvement which is apparent over the ancient plans, an improvement conducing alike to the health and comfort of the workmen. Thirty years have passed in its development, during which many difficulties arose from the conflicting opinions of the English and German glass-makers; and, in fact, it was not until the proprietors boldly separated themselves from the current and influence of old, and almost fixed opinions, that any decided progress was shown in the development of manufacturing efficiency, or any plan contributing to the health and comfort of the workmen employed.
[4] ] See drawing No. 4, at end of book.
It is to be borne in mind that the first glass works in this country were established by the Germans, who used no other fuel than wood, the furnaces for window-glass constructed under their directions being for that fuel only; on the other hand, the English workmen who introduced the making of flint-glass had made use of no other fuel than coal, and the English were therefore obliged to adopt (for the want of coal) the German plan for furnaces, and adapt the same to the making of flint-glass. The house was like the furnace, half English and half German, and from the year 1812, for thirty years, little or no improvement was made in this particular. Year after year the old plan was followed, until necessity paved the way for new plans in the effort to secure a less expensive mode of melting glass.
The result has been highly favorable. More than one half has been saved in the melt, annealing leers, and working places, yielding the workmen greater space and facilities in performing their work, and no longer exposing them to the discomfort of extra heat, smoke, and unhealthy gases. These improvements have enabled the American manufacturer to sustain his business in the severe and trying competition with foreign manufacturers, who forced their glass into this country through their agents a few years since, in such quantities, and at such reduced prices, as seriously to affect the prosperity of our artisans; yet, aided as they have been by a tariff directly promoting foreign interest, and by the very low rates of wages paid on the Continent, they have been successfully contended with, and now a home competition has sprung up, reducing prices below a fair standard,—a competition, the result of enterprise, which will, erelong, regulate itself, for we fully hold to the maxim, that competition, honest and well sustained, is the soul and life of business:—