December 6, 1889.] 



SCIENCE. 



381 



slot or small gas-chamber f g receives atmospheric air to form an 

 inflammable mixture with the gas in the small chamber through the 

 duct/- in the fixed cover b, which duct/^ communicates with the 

 port^ of the small gas-chamber/_^. 



By the action of the ratchet motion the small gas-chamber f g 

 in the disk a, having been charged in the manner described, is car- 

 ried rapidly forward, and the gaseous mixture therein is ignited by 

 the fixed relighting gas-jet /;'. The igniting of the charge in the 



small gas-chamber /_§- takes place immediately before the passage 

 h comes opposite the port d into the gas-cylinder a". The passage 

 h coming opposite the port d, the flame in the small gas chamber 

 f g ignites the gaseous mixture in the port d and the engine cylin- 

 der a?. The passage h opens into the port g of the small gas- 

 chamber/^ immediately after the small gas-chamber and the 

 port/^ are closed, the duct i communicating with the port d a little 



before the port h communicates with the port d to effect the igni- 

 tion of the gaseous mixture in the gas-chamber or cylinder (t". 



The supply of gas is regulated by the lever o and the gas-valve 

 r. The lever receives its motion through a spindle, o\, from a sec- 

 ond lever, which is acted upon by a cam on the side shaft. This 

 cam is under the control of the governor. The lever o carries a 

 cam,/', which engages with a lever,/, having at its end a stud, q^, 

 ' taking into a slot, q, in the pawl /. Upon the lever o moving 



so as to open the gas tappet-valve, the cam /' operates upon 

 the lever/, causing the stud q to be disengaged from the slot, and 

 allowing the pawl to fall into the teeth of the valve. When the 

 engine is running so fast that the gas-valve is not opened, the stud 

 holds the pawl out of gear. 



This engine has been subjected to a series of tests by Professor 

 R. H. Smith of Mason College, Birmingham, and has given most 

 satisfactory and economical results. It was tried at full working 

 load, at half load, and without load, the latter test being divided 

 into three parts, — at fast, medium, and slow speeds. The full 

 working load trial lasted 85 minutes, the speed being 176.86 revo- 

 lutions per minute. The indicated horse-power was 5.54, and the 

 brake horse-power 4.807, giving a mechanical efficiency of 0.8677. 

 The gas consumed in driving the engine was 163.2 feet, or 20.79 



Fig. 6. 



Initial pressure 220 lbs. per sq. in. 



Average mean pressure 77*73 " 



Revolutions per minute 17s 



cubic feet per hour per indicated horse-power, and 23.97 feet per 

 brake horse-power. Fig. 6 shows an average indicator card taken 

 during this trial; and Fig. 7, a high-pressure card, illustrating how 

 the governor supplies a richer charge of gas when any sudden de- 

 mand is made on the engine. At half-power, the brake horse- 

 power was 3.084, equal to a gas consumption of 31.86 feet per 

 horse-power per hour. The lighting jet burned about two feet an 

 hour in both cases. When the engine was running empty, it 

 burned 53 feet of gas per hour at the high speed, 44 feet at the 

 medium speed, and 34 feet at the low speed. A comparison of 

 these results with those obtained in the Society of Arts trial in 

 England shows that the Forward gas-engine ranks very high in 

 the matter of economy, while its mechanical simplicity is a great 

 additional recommendation. 



One of these engines, of 4 horse-power, is now on exhibition in 



Initial pressure 165 lbs. per sq. in. 



Average mean pressure 65.11 



Revolutions per minute 177 



Boston, by the Forward Gas Engine Company, who, we under- 

 stand, control the patents for this country, and will soon begin 

 their manufacture. 



A DANGEROUS INSECT PEST IN MEDFORD, MASS. 



Mr. C. H. Fernald of the Division of Entomology of the 

 Hatch Experiment Station of the Massachusetts Agricultural Col- 

 lege, Amherst, Mass., has issued a special bulletin on " A Danger- 

 ous Insect Pest in Medford," known as the gypsy-moth (Qcneria 

 dispar L.). On the 27th of last June, during his absence in Europe, 

 several caterpillars were received at the station from Hon. William 

 R. Sessions, secretary of the Board of Agriculture, with the re- 

 quest for information as to what they were, and the best methods 

 of destroying them. These caterpillars were brought into the sec- 

 retary's office by Mr. John Stetson of Medford, Mass., who stated that 

 they were very destructive in that town, eating the leaves of fruit and 

 shade trees. Mrs. Fernald, who had charge of the entomological 

 work during Mr. Fernald's absence, determined the insect to be 



