They moved in tandem without looking at each other, their movements controlled and efficient.
Typically they are steam pumps, the steam and water cylinders being set tandem on the same bed frame, generally without fly-wheel or other rotary parts; they may be single cylinder or duplex, simple, compound or triple expansion, and having a higher speed of stroke are smaller in all their parts than Cornish pumps.
Steam at high pressure exhausting into the atmosphere is still commonly used, but the great power required for raising heavy loads from deep pits at high speeds has brought the question of fuel economy into prominence, and more economical types of the two-cylinder tandem compound class with high initial steam pressure, superheating and condensing, have come in to some extent where the amount of work to be done is sufficient to justify their high initial cost.
Passing now to the invention of common or decimal logarithms, that is, to the transition from the logarithms originally invented by Napier to logarithms to the base io, the first allusion to a change of system occurs in the "Admonitio " on the last page of the Descriptio (1614), the concluding paragraph of which is " Verum si huius inventi usum eruditis gratum fore intellexero, dabo fortasse brevi (Deo aspirante) rationem ac methodum aut hunc canonem emendandi, aut emendatiorem de novo condendi, ut ita plurium Logistarum diligentia,limatior tandem et accuratior, quam unius opera fieri potuit, in lucem prodeat.
A recent feature of this machine is the tandem equipment, whereby two, three or even four machines may be coupled together for colour work.
Next to a leisurely walk I enjoy a "spin" on my tandem bicycle.
The "sociable" is safer, perhaps, than the tandem; but it is very heavy and awkward, and has a way of taking up the greater part of the road.
My teacher and other friends think I could ride a Columbia tandem in the country with perfect safety.