How Old Is the Earth? 



the Salt of the Sea 



THE salt of the ocean has been 

 made to give an answer to the 

 question of the age of the earth. The 

 general idea seems simple enough to 

 be worked out by anyone with a 

 plentiful supply of good long pencils 

 and sufficient paper. 



Salt is carried down year after year 

 into the sea, where it accumulates. If, 

 then, we can divide the entire amount 

 of salt at present in the ocean by the 

 amount carried down in a year, the 

 quotient will be the probable age of 

 the earth. Simple? Oh yes. Pro- 

 fessor Joly has worked it out to ninety- 

 nine million years, but to be on the 

 safe side he reduces that number to 

 ninety million. A little matter of nine 

 million years is negligible to those who 

 can think in such numbers. 



Popular Science Monthly 

 As Old as 



747 



The steam shovel moved along by its own power on 

 its self-laid track at the rate of about four blocks 

 a day through the side streets of the city 



Low temperature 

 contact points 



High temperature 



contact points 



The Temperature Alarm. It Tells You 

 Whether You Are Too Warm or Too Cold 



THE burglar alarm now has a rival in the 

 temperature alarm. A bell rings to 

 inform you that you are too warm, or too 

 cold, as the case may be. 



Let us assume that the damper on your 

 furnace is open, which, of course, causes the 

 fire to burn fiercely. A chain is attached to 

 the damper at one end, 

 and at the other to a 

 metallic ring. The ring 

 is part of an electric cir- 

 cuit in which the bell is 

 located. A thermostat (a 

 kind of thermometer) is 

 inserted in the circuit 

 near the contact point, 

 and swells when the house 

 becomes too hot. This 

 causes the contact points 

 of the thermostat to 

 touch, and the circuit is 

 thus closed, so that the 

 bell rings. 



Upon hearing the bell 

 ring, you realize that you 

 are too warm. You move 

 the metallic ring down to 

 another position which 

 breaks the circuit, causes 

 the bell to stop ringing, 

 closes the damper and 

 cools the house. 



A thermostat 

 (a kind of 

 thermometer) 

 inserted in a 

 bell circuit 

 causes the 

 bell to ring 

 when the 

 temperature 

 is too high 

 or too low 



How a Railroad Steam-Shovel 

 Traveled Through New York City 



IN excavating the site for a new hospital in 

 New York city a contractor made use of a 

 gigantic steam-shovel mounted on a stan- 

 dard railroad flat-car. Upon the comple- 

 tion of the work the shovel had to be trans- 

 ported to the next scene of operations, in 

 this case several miles away, the route being 

 entirely through city 

 streets. 



No alternative pre- 

 sented itself to the mind 

 of the contractor to a plan 

 to lay tracks for this 

 self-propelled steam- 

 shovel and to pick them 

 up again after the shovel 

 had passed on. So, mak- 

 ing use of three short sec- 

 tions of track consisting 

 of standard rails held 

 the required distance 

 apart by iron rods, the 

 steam-shovel started on 

 its queer journey. As it 

 passed, under its own 

 power, from the last sec- 

 tion to the second sec- 

 tion, a team of horses 

 hauled the last section 

 around to the front of the 

 shovel to form a new 

 length of track. 



