830 Transactions of the American Institute. 



where these gums, iifter eating will be filled witli comminuted food 

 and saliva. Dr. Preterre has been most successful in producing the 

 most perfect plates. 



Dr. A. Preterre remarked that by taking a series of molds each 

 larger tlian another he could enlarge the size of the tooth without 

 having the mold in sections. 



The secretary then read the following paper which occupied the 

 remainder of the e^■ening : 



THE BEST MODES OF TESTIKG THE POWEES AND 

 ECOKOMY OF THE STEAM ENGINE. 



By Charles E. Emery. 



Late of the U. S. Navy and U. S. Steam Expansion Experimcute. 



The steam engine is the only motor that has successfully cotnpeted 

 with or supplanted the changeable and uncertain power derived from 

 animal muscle, and the natural forces of wind and water ; and its 

 varied adaptations and applications have brought it into general use 

 throughout the civilized world, not only in stupendous water works 

 and manufactories, and in furnishing reliable and rapid communica- 

 tion by land and sea, but also in reducing the physical exertions of 

 both sexes in the less grand but more important operations of the 

 producing community in the forest, field and farm house. 



Surely, then, the steam engine is not an experiment. Years ago, 

 it was made a success, and soon became a necessity ; and notwith- 

 standing the grand discoveries that have been made in theoretical and 

 practical science, the steam engine has to this day remained unchanged 

 in every important particular. The principal advance has been in 

 the perfection and general adoption of the simple high pressure engine. 

 Many of the so-called improycments were mere variations in form 

 and in the details of construction, which often failed to produce as 

 economical results as older well tried mechanism. Nearly all the 

 true improvements have been in workmanship and in adaptations 

 and applications to various uses. A few of the general principles 

 which influence the economy of the steam engine have long been 

 known, and our manufacturers have in very many cases claimed a 

 superiority for their engines on account of alleged excellence in the 

 details of the valve gear, or other mechanism, designed to secure the 

 results promised by theory, forgetting that theoretical propositions 

 are of little value, unless all the conditions assumed are the same as 

 those in practice, which is rarely the case. It therefore often happens 



