ats 
beneath the seismosrapn array in shallow water and thencétonating it after 
a known time and measuring the arrival time at the various geophones. The 
first: method required & PDR and a rough bottom with many "highlights", the 
second requires a seismograph system and shallow water. 
Measurements of tilt and strain in sea ice were attempted at Station 
Alpha but the results were generally unsatisfactory. The first instrument 
was a sensitive bubble-level ease to measure tilt of the ice. Two bubble- 
levels with a long radius of curvature were mounted perpendicular to each 
other on an aluminum plate. The plate was triangular with micrometer screws 
at the acute angles to regulate the elevation of the corners. The three 
instrument legs were placed on wooden posts which had been frozen to a depth 
of about two feet in the ice. The procedure was to relevel the instrument 
twice daily with the micrometer screws anc take the reading from them. The 
readings appeared quite erratic and there has been doubt as to whether the 
readings actually represent ice tilt. It was felt that factors such as 
thermal warpine of the plate, recrystallization around the supports and 
imperfections in the screws may have produced effects as large as those 
of ice tilt. Another instrument was developed at Alpha to measure ice strain. 
This instrument was constructed by freezins two large iron pipes to a depth 
of several feet in the ice with about 30 feet of separation. An invar wire 
was attached to one post and led over a precision pulley on the other. A 
weight was attached to this end and the weight rested against a dial gage 
peuesuive to about 1074 inches. The dial gage was read twice daily. Here 
too, doubt was felt about the meaning of the experiment. Apparently the 
invar wire chosen was of too small diameter and a slow plastic deformation 
took place. In the future, it would be wise to use wire with as large a 
diameter as will freely run over the pulley. Three strain meters ina 
