The series—­consisting of cards 4x21/2 cm., each containing a printed couplet—­was carried on a car which moved on a track behind and slightly below the aperture.  The car was a horizontal board 150 cm. long and 15 cm. wide, fixed on two four-wheeled trucks.  It was divided by vertical partitions of black cardboard into ten compartments, each slightly wider than the aperture to correspond with the visual angle.  A curtain fastened to the back of the car afforded a black background to the compartments.  The couplets were supported by being inserted into a groove running the length of the car, 3 cm. from the front.  A shutter 2 cm. high also running the length of the car in front of the groove, fastened by hinges whose free arms were extensible, concealed either the upper or the lower halves of the cards at the will of the operator; i.e., either the foreign symbols or the words, respectively.  A screen 15 cm. high and the same length as the car, sliding in vertical grooves just behind the cards and in front of the vertical partitions, shut off the objects when desired, leaving only the cards in view.  Thus the apparatus could be used for all four types of series.

The method of presentation and the time conditions of the A set were as follows:—­A metronome beating seconds was used.  It was kept in a sound-proof box and its loudness was therefore under control.  It was just clearly audible to both operator and subject.  In learning, each couplet was exposed 3 secs., during about 2 secs. of which the shutter was fully open and motionless.  During this time the subject read the couplet inaudibly as often as he wished, but usually in time with the metronome.  His object was to associate the terms of the couplet.  There was an interval of 2 secs. after the exposure of each couplet, and this was required to be filled with repetition of only the immediately preceding couplet.  After the series had been presented once there was an interval of 2 secs. additional, then a second presentation of it commenced and after that a third.  At the completion of the third presentation there was an interval of 6 secs. additional instead of the 2, at the expiration of which the test commenced.

A^{13-16} had five presentations instead of three.  The test consisted in showing the subject either the numbers or the words in altered order and requiring him to write as many of the absent terms as he could.  In the object and movement series the objects were also shown and the movements repeated by the subject if words were the given terms.  The time conditions in the test were,

Exposure of a term                        3 secs. 
Post-term interval in A^{1-12}            4 secs. 
Post-term interval in A^{13-16}           6 secs.

This allowed the subject 7 secs. for recalling and writing each term in A^{1-12} and 9 sec. in A^{13-16}.  If a word was recalled after that time it was inserted, but no further insertions were made after the test of a series had been completed.  An interval of 3 min. elapsed between the end of the test of one series and the beginning of the next series, during which the subject recorded the English word of any couplet in which an indirect association had occurred, and also his success in obtaining visual images if the series was a noun or a verb series.