352 b 352 c 352 d 352 e is preferably substantially identical and includes a uniform array of apertures the apertures 354 e forming parts of the set 352 e and the apertures 354 b forming parts of the set 352 b as shown in the enlargements of fig1 are exemplary preferably the apertures of the sets 352 a 352 b 352 c 352 d 352 e including the apertures 354 b and 354 e are preferably circular and each have a diameter of between about 5 and 300 microns and more preferably between about 50 and 200 microns preferably the average diameter of the apertures of the distribution layer 350 is less than the average diameter of the apertures of the distribution layer 330 preferably adjacent ones of the apertures of the sets 352 a 352 e are spaced apart from one another a distance of between about 70 and 80 microns preferably the thickness of the layer 350 is between about 300 and 700 microns and more preferably between about 400 and 550 microns preferably the layer 350 is formed of glass silicon silicon carbide borosilicate glass polycrystalline silica ceramic plastic or photodefinable metal more preferably the layer 350 is formed of silicon with reference to fig1 the plenum layer 360 is substantially identical to the layer 340 the longitudinally extending slots of the layer 360 correspond to the longitudinally extending slots 342 a 342 b 342 c 342 d 342 e and overlie the sets of apertures 352 a 352 b 352 c 352 d 352 e respectively of the layer 350 with reference to fig1 the burner face layer 370 includes rows 372 a 372 b 372 c 372 d 372 e of apertures more.