The program, named ‘Early Journal Content’, provide access to all the collections of journals whose was published before the year 1923.
Quoting the Jstor announce:
Early Journal Content on JSTOR, Free to Anyone in World
On September 6, 2011, we announced that we are making journal content in JSTOR published prior to 1923 in the United States and prior to 1870 elsewhere freely available to anyone, anywhere in the world. This “Early Journal Content” includes discourse and scholarship in the arts and humanities, economics and politics, and in mathematics and other sciences. It includes nearly 500,000 articles from more than 200 journals. This represents 6% of the content on JSTOR.
While JSTOR currently provides access to scholarly content to people through a growing network of more than 7,000 institutions in 153 countries, we also know there are independent scholars and other people that we are still not reaching in this way. Making the Early Journal Content freely available is a first step in a larger effort to provide more access options to the content on JSTOR for these individuals.
Terms, conditions and other useful information about this program, is available through this Jstor link.