The first baseballs had anything from a walnut to a rock in the center. Yarn or string was wrapped around any solid substance. The string was then encased in leather. Players made their own or had them made for them to their own specifications. Since the custom was for the first teams of the 1850s to supply the balls for a game, games were dramatically swayed by the choice of a ball with properties that suited a team’s style of play.

In 1854, three New York teams decided they would use balls that weighed 5½ to 6 ounces. The weight changed to between 6 and 6¼ ounces three years later. In 1858, it was decided that the center be made of India rubber. In 1860, everything changed again. The official weight of a baseball was reduced back to 5¾ ounces, then to 5 ½ ounces in 1861, and to 5¼ ounces in 1867. In 1871, it was decided that the weight of the rubber inside should be no more than 1 ounce. 

The last notable change to baseballs came about in 1974 when MLB changed the outside covering to cowhide from horsehide, as horsehide became hard to come by. Major League Baseball now puts its baseballs through stringent testing before play. They are shot from air cannon at a speed of 85 feet per second at a wall of northern white ash and must rebound at no more than 0.578 percent of their original speed.

(http://www.livestrong.com/article/359789-history-of-the-baseball-ball/) Facts From