

106 LIVERPOOL BIOLOGICAL SOCIETY. 
Fig. 3 A. represents the upper half; towards the left may 
be seen the slit into which the rope passes, whilst to the 
right and below is the slip which fills up the corresponding 
gap in the lower half, a front view of which may be seen 
in fig. 3c. Fig. 3 8. shows a longitudinal section through 
the complete messenger. The top of this one is tapered 
so as to permit the other to slide over it without any 
danger of catching. 
2. The second messenger (fig. 4) precisely resembles the 
first in principle, but to either portion is attached the half 
of a brass tube, divided longitudinally so that when it is 
put together a cavity is formed in the lower part, large 
enough to enclose the first messenger. Fig. 4c. shows 
the appearance of the upper extremity of the messenger 
when put together. 
The conditions which must obtain in regard to the form 
and disposition of the upper ends of the pins (g.,g’.) can 
now easily be seen. The pin (g’.) meant to be acted upon 
by the first messenger must he near to the rope, and the 
upper curved part must embrace this so closely that the 
tube of the second messenger is sure to fall clear of it. 
The pin (g.) to be actuated by the second messenger must 
stand so far from the rope that the first cannot reach 
it, but so near that the second is sure to do so. These 
conditions are easy to secure provided the messengers fit 
the rope without too much play; but where ropes of very 
different sizes are used, it would be advisable to have a 
special set of messengers for each. The heads of the pins 
are curved round the rope as a centre so that an inclination 
of the rope obliquely to the surface of the lock shall not 
render it possible for the messengers to miss them. 
_ For experimental purposes the messengers have been 
made of lead, but for permanent use it will be advisable to 
construct them of brass, and a ring fitting into a groove, 


