Popular Science MontJily 



Which CyHiider Is Missing Fire? 

 Find Out from the Seat 



THE invention 

 shown in the 

 accompanying il- 

 lustration can be 

 used either as a test- 

 ing apparatus for 

 shop work or as a 

 permanenj; device 

 to be placed on the 

 dash of an automo- 

 bile. The chauffeur 

 can determine easi- 

 ly and quickly just 

 which one of his 

 engine cylinders is 

 missing fire with- 

 out getting out of 



Wires to spark plug 



225 



rally, if a particular cylinder is not firing 

 properly, its power will not be sufficient 

 to carry all the pistons over and against 

 the combined com- 

 pressions. There- 

 fore, by allowing 

 the current to pass 

 through each spark 

 plug, if necessary, 

 the offending one 

 caasoon be located. 

 If the cylinder is 

 firing, as it should, 

 the engine will run 

 without help from 

 the other cylinders. 



Showing the mechanism of 

 the ignition-detector. Us- 

 ing it, the chauffeur can 

 test his cyUnders with- 

 out getting out of the car 



Mandolin Music 



Via the Tuneful 



Molar 



T last someone 



A 



alindef cut 

 switches 



his seat or raising the hood over the 

 engine. The offending cylinder is de- 

 tected by shutting off the ignition 

 circuit of all the cylinders except 

 one and allowing this one to pull 

 the others against 

 compression. To 

 shut off the circuits, 

 little contact plugs 

 on the front of a box 

 on the dashboard are 

 depressed by means 

 of small handles 

 which force any par- 

 ticular strip back 

 against a bus bar at 

 the rear. When this 

 is done, the current 

 is shunted from the 

 plug through the lead 

 and bus bar back to 

 the current source 

 through the usual 

 ground wire. Natu- 



New mandolin design promises to 

 make the human tooth famous 



ed what has ailed 

 the mandolin these 

 many years. With 

 his trained archi- 

 tectural eye and his well-developed sense 

 of what's what in ornamental designing, 

 R. C. Petty, of Drumright, Oklahoma, 

 has decided that the vitals of the instru- 

 ment are in good order but the general 

 contour of the thing is all wrong. Ac- 

 cordingly, he has invented an instrument 

 which for beauty of line and lavishness 

 of design is without a peer. 



Exhibiting a marked degree of 

 originality, he has chosen the human 

 tooth for his model. 

 Look at the accom- 

 panying illustration 

 and you will see how 

 faithfully this knight 

 of the strings has fol- 

 lowed the graceful 

 outlines of the molar. 

 But he has taken 

 away none of the en* 

 trancing melodic 

 quality of the 

 instrument itself. In 

 its nevvf and more 

 beautiful shape, the 

 mandolin may be 

 said to be even more 

 tuneful, if such a 

 thing is possible. 



