110 University of California Publications in Zoology |Vou-9 
the supporting frame; the other end terminates in a binding 
post. The armatures carry slender pointers (p.), which mark 
the smoked paper of the drum. The connections with the cages 
are simple. Each lever of a cage actuates one of the two mag- 
nets. Attached to the outer end of each unpaired bar (s. br.) 
of the lever is a platinum point (pl. pt.,) which is connected by 
a wire (wy., pl. 13, fig. 2) with one fulerum-nail of the lever. A 
movable contact is thus made between the nail and the metal 
lever support (lr. sup.), which im turn is connected through a 
Fig. C. Signal magnets with attached pointers, which record on the 
chronograph drum the movements of the two parts of the floor of the cage. 
binding post at b. p. (pls. 18 to 15) with one pole of a battery. 
With each excursion of the lever the platinum point at its end 
comes into temporary contact with another platinum point 
(pl. pt..) supported on the adjustable block (bl/k.). This second 
platinum point is connected with the binding post of the 
appropriate magnet (compare pl. 14, fig. 3; pl. 13, fig. 2, and pl. 
15). The frame and support of the magnets is connected by a 
wire (c. wr., pl. 15) with the other pole of the battery. Contact 
between the platinum points completes the cireuit and the battery 
actuates the magnet, which pulls to itself the pointer (p.), and 
thus a vertical mark is made on the drum. Inspection of the 
figures will make clear these arrangements. 
The working of the machine is nearly the same as in the one 
previously described, the important difference being that in the 
present machine it is possible to determine only the passage of 
the animal into and out of the nest, whether it be before or 
after a litter is born. For further details see Long and Mark, 
ah lake 
