填空题

It was during the nineteenth century that the rapid development of the heat engine took place, and with ever increasing power at the disposal of man, the mechanical age began. The demand 41 more and more power as new industries evolved created a great incentive for invention. At first, attention was solely devoted to practical improvement, but 42 the trend was more toward philosophical reasoning, with a result that engineers found 43 necessary to review their fundamental ideas. It was seen that the consideration of practical detail 44 was insufficient in the attempt to produce more efficient machines. Theoretical reasoning was also necessary, and it was through the work of men such as Carnot, Gibbs and others, 45 the theoretical study developed. The 46 of their philosophy and the skill of the craftsmen, together with the ingenuity of the practical engineers, resulted 47 progressively more efficient engines. 48 with the prime movers of the nineteenth century, our present-day engines and power plants are very efficient. Nevertheless, design and development engineers are continually striving to produce even more efficient machines. In this task they must engage in conflict 49 the restrictions which Nature imposes upon energy conversion processes, and they must be 50 with the knowledge which is gained from the study of the subject of Thermodynamics.