488 KANSAS CITY REVIEW OF SCIENCE. 
power per hour, while consurning actually, in the best examples, about fifteen, 
z. é., with an efficiency of sixty or seventy per cent. 
In hot-air engines we are not making much more progress, and our field of 
promise seems to be still in the improvement of the steam engine. 
We are slowly learning other facts. We know that the great obstacle in the 
way of attaining nearly theoretical efficiency is the transfer of heat from the 
steam to the exhaust side by initial condensation and re-evaporation ; we are 
discovering that high speed and steam jacketing tend to lose their efficiency at 
extremely high pressure with wide ranges of expansion, that it seems possible to 
reach a point in steam-jacketed cylinders at which lower speed may tend to se- 
cure efficient working of the steam; that with well-jacketed cylinders we may 
get good performance, as we to-day judge it, with slow pistons; that we have bet- 
ter work claimed to-day for single than for ‘‘compound ” engines by ten or fifteen 
per cent., §$the minimum yet reached under fair conditions for economy being 
stated to be by experiment as 1.54 is to 1.75, while, assuming the very best con- 
ditiovs for each, it seems certain that both types should give about equally good 
results. | 
Here is where we stand to-day, and it is from this point that we are to work for- 
ward. We need to collect more facts by means of carefully-devised experiments 
like those of Hirn and Hallauer abroad, and of Emery and the Navy Department 
at home; we need careful and systematic study of the results and finally the de- 
termination of the laws of steam engine efficiency as affected by steam pressure 
and temperature, rates of expansion and compression, character of steam jackets, 
rate of piston speed, and every other circumstance influencing economy. 
INS NIE OUNIO) IMIG, 
PLANETARY AND STELLAR PHENOMENA FOR DECEMBER, 188o. 
BY W. W. ALEXANDER. 
Mercury rises on the 1st at 5 h. 44 m. a. m. and on the 31st 6 h. 21 m.a. m. 
and is at its western elongation on the 21st, at which time it can be best observed, 
being then in the constellation Scorpius about 7° north of Antares. 
Venus sets on the 31st at 6 h. §8 m. p. m. and on the 31st at 8h. 03 m. p. 
m., and is fast increasing in size and brilliancy. 
Mars rises on the 1st at 6 h. tom. a. m. and on the 31st at 5 h. 56 m. a. 
2 Abstracts of Papers, No. 1602; Proc. Brit. Inst. C. E., Vols. LIII, LIV. It would seem that where 
slow piston-speed is demanded, as usually with pumping engines or where two cylinders are needed as with ma- 
rine engines, the ‘‘ Compound” engine is unmistakably best; while where high-speed engines are permitted, as 
in mills, the single-cylinder may still hold its own in this competition. 
