T HE LIGHTNING-STROKE generator has made samples indicating the area "blown" are shown in figure 3. possible the investigation of lightning-stroke phe-For rather strong, yet quite thin, white paper (first 8 nomena in the laboratory."'2 This paper deals with samples), the average area "blown" for a current of 53,000 the fundamental aspect of the problem, particularly with amperes (average) is close to 0.15 square inch. One test the characteristics of the lightning-stroke channel. The at 23,500 amperes gives an area of 0.07 square inch. On data and findings here presented reveal further the nature thicker paper (samples 12, 13, and 21) the area is 0.16 of the channel core and of the resulting column.3 Field square inch for 55,000 amperes. At higher currents, tests observations are also indicated for comparison, to enhance on the heavier paper only were possible because of tearing. the value of the laboratory investigation.An area of 0.24 square inch is obtained with 74,000 amperes (samples 15 and 16). The areas "blown" in the Test Method paper for currents of 24,000, 54,000, and 74,000 amperes are then, respectively, 0.07 square inch, 0.15 square inch, The lightning-stroke generator consists of a high-voltage generator, a heavy-current generator, and a "nmicrosecond switch." A steep-fronted high-voltage impulse from the voltage generator initiates flashover or dielectric breakdown of the test object. Then, within a time measured in microseconds the current generator is switched on thus supplying to the test object a current of lightning-stroke intensity and duration.A lightning-stroke test is illustrated in figure 2. The voltage generator first breaks down the 36-inch rod-toplate gap, this occurring on the front which rises at somewhat more than 3,000 kv per microsecond ( figure 1D). Then, as oscillogram A shows, the "microsecond switch" operates and in 5 microseconds the current generator begins discharging across the gap a current which reaches 57,000 amperes and of a total duration of 100 microseconds or more. More rapid and slower follow-up of the current occurs, respectively, for oscillograms B and C. A lightning-stroke to a distribution-line wood pole appears in figure 9 in which case the voltage to break the pole down rises to 2,500,000 volts, followed by the current of lightning-stroke intensity and duration. These tests are typical Figure 1. Voltage and current oscillograms oF lightning. of the lightning-stroke testing in this investigation. stroke tests Characteristics of Lightning Channel and 0.24 square inch, that is, the area is proportional to TESTS ON PAPER AND SIMILAR MATERIALS the current of the discharge.A blast effect is also present on the specimens. It is inThe results from tests on paper and similar materials the nature of a surface "erosion" resulting from the are summarized in table I. In these tests a large sheet combined action of the blast and the associated high temwould be mounted on an insulated wood frame and inperature. This blast effect extends out radially from the serted in the...