. ▁He ▁also ▁studied ▁the ▁first ▁games ▁that ▁b ab ies ▁and ▁children ▁play , ▁and ▁wrote ▁a ▁more ▁mathematical ▁section ▁" On ▁the ▁re bound ing ▁of ▁tennis ▁balls ". ▁As ▁with ▁his ▁bi ological ▁works , ▁the ▁Book ▁of ▁Games ▁is ▁organ ised ▁on ▁the ▁empir ical ▁principles ▁of ▁observation , ▁description , ▁and ▁classification . ▁ ▁A ▁lost ▁work ▁appears ▁to ▁have ▁been ▁one ▁that , ▁according ▁to ▁his ▁daughter ▁Cass andra , ▁" she ws ▁the ▁ch ances ▁of ▁most ▁games ", ▁which ▁may ▁have ▁been ▁titled ▁The ▁Book ▁of ▁D ice ▁(" H istor ii ▁Chart itud ii "). ▁Will ugh by ▁was ▁a ▁compet ent ▁math ematic ian , ▁and ▁there ▁is ▁evidence ▁that ▁the ▁lost ▁text ▁considered ▁probability ▁with ▁regard ▁to ▁card ▁and ▁dice ▁games . ▁ ▁Illustr ations ▁and ▁sources ▁The ▁numerous ▁pl ates ▁illustr ating ▁the ▁species ▁in ▁the ▁bird ▁and ▁fish ▁books ▁came ▁from ▁a ▁number ▁of ▁sources . ▁Will ugh by ' s ▁own ▁extensive ▁collection ▁included ▁paint ings ▁he ▁had ▁bought ▁on ▁his ▁European ▁travel s , ▁and ▁he ▁also ▁borrow ed ▁pictures ▁owned ▁by ▁friends ▁like ▁Ski pp on ▁and ▁Sir ▁Thomas ▁Brow ne . ▁Many ▁illustr ations ▁were ▁taken ▁from ▁previous ▁publications ▁by ▁other ▁writers , ▁and ▁some ▁were ▁based ▁on ▁Francis ▁Bar low ' s ▁oil - p aint ings ▁of ▁birds ▁in ▁Charles ▁II ' s ▁av i ary ▁in ▁St ▁James ' s ▁Park . ▁ ▁The ▁illustr ations ▁taken ▁from ▁earlier ▁books ▁were ▁from ▁many