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THE POPULAR SCIENCE MONTHLY. 



lire of these objects are simply ingenious modifications of those 

 involved in processes already described. Most of the scientific 

 apparatus in glass is brought from Thuringia. Our own work- 

 men do not seem to have that turn for science which is shown by 

 the Germans. Even the little apparatus which is made in this 

 country is for the most part the work of foreign artisans. 



It would be a grave omission to close even so brief a summary 

 of the office served by glass in science without calling attention 

 in a few words to one of the latest and most interesting lines of 

 research which it has made possible. We refer, of course, to the 

 vacuum tubes employed by Mr. Crookes in his well-known investi- 

 gations into the properties of radiant matter. We have been ac- 



Fm. 9. Vacuum Tubes. 



customed to talk somewhat glibly about the three states of mat- 

 ter. To this list we are now asked to add a fourth, the radiant. 

 Faraday's hint and the work of Mr. Crookes have well-nigh es- 

 tablished the distinction between gas and radiant matter. In a 

 gas under ordinary tension the molecules are in sufficient number 

 to suffer almost constant collision with one another ; but if the 

 tension be low enough, say the one five-millionth of an atmos- 

 phere, the collisions become infrequent, and the molecules travel 

 in almost uninterrupted straight lines until they come into con- 



