LANGLEY LEFFMANN. 161 



considerable size. For all the machines ho made Langley coined 

 the word " Aerodrome," from two Greek words meaning " air run- 

 ner." This word is now often used as the name for the shed in 

 which the flying machine is stored. 



In passing from very small machines in which twisted rubber or 

 steel springs can be used, which are mere toys, to large machines 

 which can make reasonably long flights, the question of motor be- 

 came of great importance. Questions of stability, both lateral and 

 longitudinal, also required answer. I will not enter into a considera- 

 tion of stability problems. They were most carefully investigated 

 by Langley, and involved mathematical as Avell as mechanical 

 methods. It is now T well known that the stability of aeroplanes has 

 been satisfactorily attained. 



When Langley began his experiments the only motor that seemed 

 to offer practical application was the steam engine. This had been 

 for a long while the only one applicable to a moving object, as is 

 indicated by its extensive use in both land and water transportation. 

 The steam engine is heavy, and also requires fuel and water, so 

 that the total weight is considerable. In the ordinary uses of it in 

 land transportation this is not a very serious matter, for the locomo- 

 tive draws best when it presses strongly on the rails, and even in 

 water transportation the weight of engine, fuel, and water are 

 probably of less importance than the space they occupy. Langley, 

 in 1891, canvassed the portable motors then known. These were, in 

 addition to steam, compressed air, liquid carbon dioxid, electric 

 batteries, gunpowder, and the internal-combustion engine. The last- 

 named, which is now the only motor used in flying machines, was 

 at that time but little developed, and was rejected, as were all the 

 others except the steam engine. The requirements were that the 

 apparatus should be light, capable of developing steam rapidly and 

 at considerable pressure, and using a fuel of high heating efficiency. 

 Water-tube boilers were alone suitable, alcohol or gasoline as the 

 fuel. Oscillating engines were used at first. Many experiments 

 were made with boilers and with burners, and much difficulty was 

 experienced in getting and maintaining sufficient pressure. Langley's 

 accounts of the failures and disappointments make painful reading, 

 but space does not permit a summary of these matters, especially as 

 the steam engine has ceased to be important in the field with which 

 we are now concerned. 



After many months of weary working it was finally thought to 

 be possible to secure a flight in the open air, and preparations were 

 made for this. The story of the failures, disasters, and disappoint- 

 ments that preceded the actual flight — told with much vividness in 

 the " Memoir " — is a striking instance of the will power and self- 



