International projectionist (Jan-Dec 1939)

.002952; in other words, .002952 is the quotient of .2501 divided by 84.72. Without further ado let's leave division and consider the method of raising a number to a power. The rule is: The logarithm of a number raised to a power is equal to the power (i.e. exponent) times the logarithm of the number. Writing this rule in general symbols: log N* = (x) (log N) Taking as a specific example the problem (6794) 2-3, we write: log (6794) 2-3 = (2.3) (log 6794) = (2.3) (3.83213) = 8.81390 hence (6794) 2S = antilogarithm of 8.81390 = 651,483,333 Following is another example, a little more difficult. Find the value of (.065) 15: log (.065) 15 = (1.5) (log .065) = (1.5) (1.81291) You can't multiply by 1.5 directly, for the logarithm is composed of a negative and positive term, the characteristic and mantissa, respectively. The way to handle this is simply to multiply the characteristic and mantissa separately by 1.5, and add the products, thus: (1.5) (2) (1.5) (.81291) hence (.065) 15 3. 1.21936 2.21936 antilogarithm of 2.21936 .0016572 To wind up the whole subject there remains only the topic of roots to entertain. The general rule is: The logarithm of the root of a number is equal to the logarithm of the number divided by the index of the root. Writing this in general symbols: log VN logN LOCAL 37 REGAINS AUTONOMY Coincidentally with announcement of a 10% tilt in pay for I. A. cameramen was the news of the return of local autonomy to Local 37, comprising studio workers, the largest single I. A. unit. Local 37 reassumes jurisdiction over studio electricians (whose Local 728 is now disbanded) and will have concurrent jurisdiction over prop makers and miniature men now in Local 44. John F. Gatelee, I. A. representative on the Coast for months past, has returned East. Suppose we have. , say, V1941 log3\/1941 = log 1941 3 3.28803 3 = 1.09601 Hence: 3yl941 = antilogarithm of 1.09601 = 12.474 That's straightforward enough. But we have to proceed in a specialized manner when the characteristic is negative. As an example, find the value of 1:t\/-49. log .49 log 1:V.49 = 1.1 1.69020 numerator is made up of two terms of opposite sign. The "out" is to add negative units or parts of units to the characteristic which will make it evenly divisible by the index of the root; and add the same number of positive units or parts of units to the mantissa. Divide those sums separately by the index of the root. The quotients are the Characteristic and Mantissa, respectively, of the logarithm sought: I. + .1 1.1 Characteristic = = = 1. 1.1 1.1 Mantissa = .69020 + .1 .79020 1.1 1.1 = .71836 1.1 We can't divide directly because the Hence: logarithm of X1\/A9 = 1.71836 Hence: 1-1\/A9 = antilog of T.71836 = .52282 With that, you can pull the cover over your microscope, place the hypo needle back in its case, unlimber your smock, and hope the injection "takes". (THE END) Causes, Effect, Aid for Electric Shock Electric shock may be divided into two broad classes: those due to current from a continuously operating source, and those due to current from a sudden discharge. First, the current from a continuously operating source will be considered. These sources include power lines, whether a.c. or d.c, transformers, rectified power supplies after the initial contact, etc. The most commonly accepted causes of death from electric current may be divided into three classes. First, the current may cause the heart or brain to lose its power to react to a stimulus. Second, metabolism in the body may be so accelerated that the blood is deprived of its supply of oxygen, and asphyxiation results. Third, sudden violent muscular contractions may cause fatal hemorrhages in various parts of the body especially in the brain. • The Danger Line Artificial respiration* may be effective in restoring life in the first two instances and especially in the second. The first two causes result usually from more or less prolonged passage of current, while the third is usually the result of a sudden heavy current. The path which the current takes determines to a large extent the effect on the body. A path through the heart is usually much more dangerous than other paths. The current which may safely be passed through the body depends on the frequency. Frequencies of 50 to 150 cycles are the most dangerous. Direct current is considered to be equivalent to *For the proper procedure to follow in case of a severe shock, readers are referred to "Resuscitation from Electrical Shock." by C. B. Desoto, p. 16, Feb., 1939, QST.— Editor. a.c. at 350 cycles. The human body readily tolerates the following for considerable periods of time: 8 ma. at 60 cycles, 30 ma. at 11,000 cycles, 800 ma. at 100,000 cycles, and 3,000 ma. at 1,000,000 cycles. While there is no close agreement by various investigators in the field, some sort of weighing of the available information would lead to the conclusion that 75 ma. of 60-cycle current and 150 ma. of d.c. should be considered as a dividing point between safe and dangerous currents. The resistance which the human body presents to an electric current depends largely on the skin resistance and hence on the type and area of contact. In general it varies between 5,000 and 100,000 ohms in actual cases with something of the order of 30,000 ohms being average. Direct current usually kicks the subject away from the circuit; while a.c, especially at frequencies around 60 cycles, causes the subject to cling tighter to the circuit. Prolonged contact with the circuit usually causes more and more current to pass due to the breaking down of skin resistance. Above 50,000 cycles the muscular contractions disappear. In 1934 the census of the United States showed that 442 people were killed by lightning and 723 by electric currents in that year. Insurance companies state that 50 per cent of electric accidents are fatal. Danger from condenser charge has not been very well investigated. An early investigator found 400 joules fatal to a 1-pound guinea-pig and concluded that the number of joules in the charge were more important than the voltage or initial current.— Communications. OCTOBER 1939 19