When the waves are convergent and the recipient screen is placed so as to contain the centre of **convergency** - the image of the original radiant point, the calculation assumes a less complicated form.

The tests for **convergency** are as follows: Let the continued fraction of the first class be reduced to the form dl+d2 +d3+d4+ then it is convergent if at least one of the series.

His treatises and contributions to scientific journals (to the number of 789) contain investigations on the theory of series (where he developed with perspicuous skill the notion of **convergency**), on the theory of numbers and complex quantities, the theory of groups and substitutions, the theory of functions, differential equations and determinants.