Shortly after this, Prof. Moses G. Farmer, a distinguished American inventor and investigator, constructed an electro-magnetic locomotive, which drew a little car, and carried passengers, on a track a foot and a half wide. The locomotive used about fifty Grove cells, which developed a relatively small amount of energy at an enormous cost. "In 1850-51," says Martin, "Mr. Thomas Hall, of Boston, exhibited a small working-motor on a track forty feet long, at the Mechanics' Charitable Fair in Boston, and while this was a mere toy, and used but a couple of cells of battery, it sufficed to illustrate the principles of a motor or locomotive with a single trial car. About this time (1847) an interesting demonstration was also made with a small working-model, one of the features of which has been most instrumental in the success of the modern electric methods, that of the utilization of the track as part of the return circuit for the current. Doctor Colton, once a famous dentist in New York City, and noted for his early application of laughing-gas in that work, was associated with Mr. Lilly in the construction and operation of a small model locomotive which ran around a circular track. The rails were insulated from each other, each connecting with one pole of the battery. The current from the battery was taken up by the wheels, whence it passed to the magnets, upon whose alternating attraction and repulsion motion depended; then it returned to the other rail, connected the other pole of the battery, and thus completed the circuit necessary for the flow of the current. In like manner in a great majority in use at present, the current passes from one power-house to circuits of one polarity, through the trolley pole to the motor or electro-magnetic propelling system, thence through the wheels to the track, which completes the circuit by being connected to the other pole or side of the dynamo at the power-house. The principles are obviously identical, but it took more than a quarter of a century to develop the proper method of application in all its details. "The most serious and sustained attempt in the early period to operate a self-sustained vehicle or car--which would correspond with the storage-battery cars--was that due to Prof. C. C. Page, of the Smithsonian Institution. About 1850, Professor Page devoted considerable time to the development of electric engines or motors, in which the reciprocating action of a system of magnets and solenoids or armatures was applied by crank-shafts to driving a fly-wheel, to which rotary motion was thus imparted. This reciprocal motion, as in steam-engines, was one of the prevailing features of the early electric-motor work in this country and in Europe; but it was not long before its general inapplicability was realized, and it was abandoned for the simpler and more direct rotation of the armature before or between the poles of electro-magnets.