438 THE POPULAR SCIENCE MONTHLY. 



works were operated entirely with wood. The same practice pre- 

 vailed in Europe, and for many years wood was preferred to coal. 

 This made it necessary to establish glass-houses near the forest 

 districts, for in the absence of railroads and of steam navigation 

 it was impracticable to carry so bulky a fuel for any great dis- 

 tance. With the substitution of coal a new condition was intro- 

 duced, and the question of fuel became for the time of less moment 

 than the supply of crude materials. These could only be obtained 

 in certain localities, while the fossil fuel was available in many. 

 In our own day, and within the last half dozen years, another and 

 much greater disturbance of the industrial equilibrium has been 

 brought about by the displacement of coal by natural gas. It is 

 no exaggeration to say that, as far as quantity and the perfection 

 of the processes of manipulation are concerned, the development 

 of the glass industry has been greater, since the introduction of 

 natural gas than in all previous time. The immense advantage 

 of the fluid fuel over the solid, both in economy of operation and 

 superiority of product, has made the geography of the glass in- 

 dustry and of natural gas nearly identical. One might almost 

 use a geological map of the United States for a chart of the glass- 

 making districts. Wherever the Trenton limestone and the upper 

 coal measures are near the outcrop, one may reasonably expect to 

 find glass-houses scattered over the surface. 



It does not follow, of course, that glass-making at the present 

 day is limited entirely to the natural gas country. There are 

 occasional glass-houses in various localities, and there are districts 

 so favorably located in other respects that they can overcome the 

 disadvantages of the solid fuel and still rank as recognized centers 

 of the industry. Such a center is found in the large bottle-making 

 establishments in southern New Jersey. But these works are 

 generally quite old, and already had expensive plants in operation 

 before the utilization of natural gas. 



The character of the fuel has thus given rise to three distinct 

 eras in the industry — that of wood, of coal, and of gas. The use of 

 petroleum has been too limited and for too secondary purposes to 

 mark a distinct chapter. 



The fourth essential element is labor. While it is, in a tech- 

 nical sense, the most important element of all, it has had much 

 less influence than the material factors in deciding the history of 

 the industry. Since its emancipation from serfdom, labor has 

 displayed a portability which has made it available in any quarter 

 of the globe. A large degree of dexterity, if not of intelligence, 

 is needed in the glass- worker ; but if one is to judge from the 

 mixed nationality of our American representatives of the craft, 

 he does not belong to any country, and is ready to go wherever 

 he is wanted. It is easier to bring him to the work than to take 



