November 29, 1901.] 



SCIENCE. 



859 



is thought to have 'had some small share iu 

 aiding the formation of a lake basin here as 

 elsewhere along the piedmont belt ; but the 

 evidence of this is in chief part borrowed from 

 the district of Lake Zurich, and that evidence 

 has been somewhat discredited, as far as lake- 

 making is concerned, in recent years. A chapter 

 is given to the systematic relations of the lake ; 

 the element of time, or stage of development, is 

 given too small a share in the proposed classifi- 

 cation. Neither the interglacial valley in the 

 Deckenschotfcer nor the later glacial advances 

 are described in terms of youth, maturity or old 

 age. Temperature, color, transparence, waves, 

 currents, changes of level, and composition are 

 all duly considered. The monograph as a whole 

 is very clearly written ; its chapters are closed 

 with concise summaries, and it has current page 

 headings and an excellent index ; advantages 

 that do not always accompany scientific publica- 

 tions. W. M. Davis. 



TRERM0DYNA3nCS OF THE GAS-ENGINE. 



The second report of the Gas-Engine Com- 

 mittee of the Institution of Mechanical En- 

 gineers of Great Britain was presented on the 

 18th of October by Professor Burstall, of Bir- 

 mingham University, and the results of experi- 

 ments, preparations for which were described 

 in the first report {Proceedings, 1898) were 

 given. They involve some important details 

 of a novel character and throw some light upon 

 previously obscure points in the theory of that 

 now important prime mover. 



Illuminating gas was employed having a 

 mean heating value of about 4.8 calories per 

 liter. A new form of igniting apparatus per- 

 mitted the ignition of even very weak charges 

 with completeness and certainty, the current 

 being obtained from four cells of the storage 

 battery, with a low voltage and a compara- 

 tively heavy current, insuring a * short and 

 thick ' spark. 



Varying compression was adopted to deter- 

 mine the effect of such variation upon the effi- 

 ciency of the motor, and, with each compression, 

 varying mixtures of air and gas, changing 

 about one per cent, at each new series of tests, 

 supplied data for ascertaining the relative 

 values of these mixtures. 



For the first time, so far as the writer is 

 aware, the theory of the gas-engine as here 

 applied was constructed with the assumption 

 of a variation of specific heats with tempera- 

 ture, following MM. Mallard and Le Chatelier. 

 The following are Professor Burstall's formulas : 



Kv^a + sT] Kp = b-\-sT; 

 Kp — jfo = const. = 6 — a~ B. 



m={w^^w^) r\a + sT)6T; 



=: (wi + w,) [a( T., —T,) -f s/2 • ( T,^ - T,')]. 



Rp = (wi + w,) P (6 + sT) 6T ; 



where H„ and Hp are the quantities of heat 

 added during the periods of constant volume 

 and constant pressure, respectively ; Wi and Wj 

 are the weight of air and gas, and the weight 

 of residual products from the previous stroke 

 in the clearance spaces. 



The equation of the adiabatic also differs 

 from that for constant values of specific heats, 

 thus : 



dTidp = vlB ; dTldv=plB ; 



^q = R.vlB ■ dp + KppjR ■ <^v = 0. 



(a 4- sT)vdp +{b-\- sT)pdv = 0. 



(6 — a) logaf -{-aloge (pv) -{-spvlB=: const. 



pOjj5g8 



B 



■ constant. 



The correspondence of the actual expansion 

 lines of the inrlicator diagram with the adia- 

 batic for variable specific heats was found much 

 closer than for the usual assumption of con- 

 stant values with varying temperatures. In 

 the computations of the heat-balance the usual 

 method would give results about fifteen per 

 cent, lower than with variable specific heats. 



The entropy equation becomes, iu the latter 

 case. 



. = a loge -1^ -f i2 log, ^ -f ;S ( r- To) ; 



'0 



T, 



where V and Fq are the volumes at tempera- 

 tures Tand Tq, respectively. 



