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An electroni c instnllncn t is described whic h p crmits sol ut ion of l rans ien t h eat-flow p roble ms by use o f direct a na logy t o electrical networks . Th e instrum en t is of t he so-called " fast-t ime" type, simulat in g t he t ransie nt involved in times of th e order of 10-6 t hat of t he ther ma l prot otype. A p hotoformer type of inp ut-signal generation is ubed and t his, togeth er wi t h a va ri a b le-frequ e ncy maste r oscillator, permi ts fl exi b ility of in p u t-sig nal wav eform a nd time scale.Some ap plications of t he in strum ent to t he fi eld of fire research are desc ri bed . The di scu ssion of e rrors includes consideration of t hose res ultin g from t h e lumping of circui t cle men ts.

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R esults of exp erimental d eterminations of the kinetic constants of the self-heating reaction are presented for wood fib erboard, cotton linters, sugar pine, cork, crepe rubber, GRS rubber, natural, synthetic, and blended foam rubber (with and without additive), various oils (raw linsecd, cottonseed, rapeseed, sperm, olive, castor, and neatsfoot) applied to cotton gauze in a ratio of 1. part of oil to 6 parts of cotton b y weight, ammonium perchlorate, and nitrocellnlose plastic. Under the assumption that self-heating follows a first-ord er r eaction, these constants were used to calculate the critical radii of spherical piles for each of four surface temperatures likely to be experi enccd in long-period storage. Calcuhted self-ignition temperatures of piles of ~~-inch-diameter to 22-inch-diameter spheres of wood fiberboard and JIg-inch-diameter to 2-inch-diameter sph eres of cotton linters were in r casonable agreement with previous mcasurements by N. D. Mitchell (National Fire Protection Association Quarterly