diameter and 5/15 in. high), positioned in a quadralateral about 2% in. ona side. The cups were coated on the inside with silicone grease to produce a tacky surface, This tacky surface held almost all particles which came in contact with it; raimvater collected during the sampling interval would not wash particles from the tacky surface un~ less the particles themselves were soluble. An S<oz jar was fastened beneath an opening in the bottom of the tray to collect liquid fallout (Fig. 2.4). A door covered the sampling opening both before and after the sampling time (Fig.2.5). The instrument was started by an external timing signal. a delay of 1 min,the cover door opened sampling position. After and the first tray moved into Succeeding trays moved into position under the cover opening at set tim intervals until the cycle was completed; (Fige 2e6)« The door then closed and the sachine shut itself off. At the time of the detonation an external timing signal actuated self-latching signal relsy Ry, (Fig. 2.7). Current then flowed through the clock which had been pre-set for a short time delay before the door opened (Fig. 2.8). At the end of this delay microswitch in the clock was tripped, allowing the current to flow through the driving motor which in turn rotated the spider; the door opened and tray 1 moved into sampling position. Sirre microswitch 53, underneath the spider rim was nec longer closed by one of the cams on the spider, microswitch Cy opened. ‘this removed the current fron the clock coil and reset the clock. The driving motor continued to run until the cam under the next tray moved over S3, When S, closed, the current path to the driving motor was broken and the motor stayed off until the clock finished another cycle. Succeeding trays moved into vosition under the cover cpening at set time intervals until the sampling cycle was completede At the time of detonation a spring cam was resting on a misro- switch S,; completing the circuit through the contact points of electrical latching relay Rj. As the cycle progressed, the spring cam rode over the microswitch, 55, completing a circuit through R3, which was thrown and latched. After the last tray was in sampling position and the door closed, the spring cam again rode over Sy, breaking the circuits and stopping the instrument. Push-button switch, S,, was used as a reset switch so that the operator could easily reset the entire instrument by one simple operation. Toggle switch Sj was mounted under the clock and was used to preset the glock. This switch remained closed during the entire opera~ tion. Resistor Ny controlled the driving motor speed to keep the trays from overshooting their position. Variable l-ohm resistors and also lengths of nichrome wire were used. 203 TIMING Where wire timing signals were available at a station, a minus l-sec signal supplied by Edgerton, Germeshausen, and Grier (EG&G) was used to actuate the IFC. Where no wire timing signals were available at a station, an EG&G Mark TII or Mark IV battery~powered blusbox was used to actuate the IFC. Wire timing signals were initially used, 18