40 .-- Impact testing machine.] The weight is lifted by a chain, one end of which passes over a sprocket wheel in the hoisting mechanism.

On the lower end of the chain is hung an electro-magnet of sufficient magnetic strength to support the heaviest striking weights.

When it is desired to drop the striking weight the electric current is broken and reversed by means of an automatic switch and current breaker.

The height of drop may be regulated by setting at the desired height on one of the columns a tripping pin which throws the switch on the magnet and so breaks and reverses the current.
There are four striking weights, weighing respectively 50, 100, 250, and 500 pounds, any one of which may be used, depending upon the desired energy of blow.

When used for compression tests a flat steel head six inches in diameter is screwed into the lower end of the weight.