"It is now quite lawful for a Catholic woman to avoid pregnancy by a resort to mathematics, though she is still forbidden to resort to physics or chemistry"

This quote by H. L. Mencken is referring to the Catholic Church's stance on contraception. In the past, the Catholic Church has been opposed to contraception, but this quote suggests that the Church has become a lot more lenient in its position. Mencken is stating that it is now acceptable for a Catholic woman to use mathematics to stay clear of maternity, however she is still not enabled to utilize physical or chemical techniques. This could suggest that the Church is currently allowing the use of all-natural household preparation techniques, such as the rhythm method, which include tracking a female's menstrual cycle and calculating when she is more than likely to conceive. This quote suggests that the Catholic Church is coming to be more open up to the suggestion of birth control, but is still not willing to totally accept it.