Popular Science Monthly 



433 



For example, you wish to ascertain the 

 latitude of San Francisco, and make your 

 observation on October 23. 



1. Ascertain your north-south line. 

 (The sun's shadow will cross it on that 

 date at 11 h. 54 m. 33 s. A. M., Pacific 

 time.) 



2. The sun's altitude, when the shadow 

 is north, would be found to be 41°. 



3. The declination is 11° S. Adding, 

 we get 52°, the altitude of the celestial 

 equator. 



4. Subtract: 90° — 52° equals 38°, 

 the latitude of the place of the observer. 



The "analemma" employed is a care- 

 fully worked-out diagram, giving the 

 position of the apparent sun and its 

 declination for every day in the year. It 

 must be remembered that, each year, this 

 will vary slightly, but for all ordinary 

 calculations, the diagram here given will 

 answer every purpose. 



The vertical lines represent the number 

 of minutes the apparent sun is slow or 

 fast — as compared with the mean sun. 

 Since the analemma shows how fast or 

 slow the sun is each day, it is obvious 

 that, knowing one's longitude, one can 

 set his watch by the sun, by reference to 

 this diagram ; or, having correct clock 

 time, one can ascertain his longitude. 



To ascertain longitude, one must have 

 a true north-south line ; also the correct 

 standard time. Now — 



1. Note when the .sun's shadow is due 

 north. Refer to your analemma and see 

 how far the sun is fast or slow. 



2. If fast, add the amount to the time 

 by your watch; if slow, subtract. This 

 gives you mean local time. 



3. Divide the number of minutes and 

 seconds past or before 12 by 4. This Avill 

 give you the number of degrees and min- 

 utes you are from the standard time 

 meridian. If the right time is before 12, 

 you are east of it; if after, you are west 

 of it. 



4. Subtract (or add) the number of 

 degrees you are east (or west) of the 

 standard time meridian, and this gives 

 you your longitude. 



To set your watch you must have a 

 correct north-south line and know your 

 longitude. 



1. Find the difference between your 

 longitude and that of the standard time 

 meridian by which you wish to set your 



watch — Eastern time. Central time, etc. 

 — as the case may be. 



2. Multiply the number of degrees and 

 seconds of the difference by 4. This 

 gives you the number of minutes and 

 seconds your watch is faster or slower 

 than local time. If you are east of the 

 standard meridian, your watch must be 

 set slower than local time ; if west, faster. 



3. Observe the position of the sun — 

 whether fast or slow — according to your 

 analemma. If fast, subtract that time 

 from the time obtained in step two ; if 

 slow, add. This gives you the time be- 

 fore or after 12 when the shadow will 

 be north; before 12 if you are east of 

 the standard time meridian; after 12 if 

 you are west. 



4. Set your watch at the time indicated 

 by step 3, when the sun's shadow crosses 

 the north-south line. 



To strike a north-south line you must 

 know your longitude and have correct 

 time. Steps, 1, 2 and 3 are just the 

 same as before (in the last example). 

 At the moment of making step 3, you 

 know the shadow is north ; then draw 

 the line of the shadow. If out of doors, 

 stakes will indicate this line. 



A Vulcanizer for Tire Repairs 



SEVERAL new 

 types of vulcaniz- 

 ing devices have re- 

 cently been placed on 

 the market for the 

 motorist who desires 

 to make his own 

 quick tire repair on the road. They all 

 naturally strive to utilize some material 

 or part of the car. Among those of more 

 than passing interest is one which can 

 be used without special instructions. It 

 is nothing more than a clamp, in which 

 the inner tube is held. On the upper 

 half of this clamp is a hollow, to be filled 

 with gasoline. A one-ounce measure 

 goes with the device, and thf ounce of 

 gasoline will burn about seven minutes, 

 which is just enough to effect a complete 

 repair of a puncture. 



Another device consists of a plain 

 metal plate which is held by any sort of 

 clamp to the exhaust pipe of the muffler. 

 Putting the inner tube on this metal plate 

 and holding it down on it for about five 

 minutes is sufficient for vulcanizing. 



