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in their faculties, passions and propensities; or if there was a diversity 

 what was its nature and extent; and the-.result of the investigation 

 seemed likely to shed no little light on the several theories, which 

 have been put forth to explain the diversities of genius and mental 

 character. 



It is known that some maintain with Helvetius, that these diver- 

 sities among men whose organs have the ordinary degree of sound- 

 ness, are the result of the particular circumstances in which the diffe- 

 rent individuals chance to be placed, while others insist that the cause 

 of such diversities is to be attributed mainly to a difference of orga- 

 nization. Of this opinion was Dr. Gall, who further maintained that 

 the mental faculties and propensities of each individual were indi- 

 cated by small protuberances at the surface of the brain, and that 

 these might be discovered by means of correspondent protuberances 

 on the skull. There is a third class comprehending a much larger 

 number both of vulgar and philosophic minds, who think that our in- 

 tellectual character depends partly on nature and partly on cultiva- 

 tion, and who would apply to mental excellence of every kind, what 

 Horace says of poetical genius : 



ego nee studium sine divite vena,, 



Nee rude quid prosit video ingenium, alterius sic 

 Altera poscit opem res et conjurat amice. 



Now, if it should be found, on a careful comparison of the two 

 brothers, that notwithstanding they had been placed in precisely simi- 

 lar circumstances, there was a marked difference in their faculties 

 and tastes, they would seem to afford a satisfactory refutation of the 

 doctrine of Helvetius. Should, however, no difference be discovered 

 in their mental powers and propensities, then indeed, we should not 

 be able to decide whether this close resemblance was to be attributed 

 to the identity of circumstances in which they had been placed, or to 

 that similarity of organization which is often seen in twins, and which 

 nothing since their birth could, in this case, have disturbed. 



To compare the minds of two persons whom we had so much rea- 

 son to expect would think and feel alike, it occurred to me that the 

 most eligible plan would be to propound the same questions at the 

 same time to both, to take the answers of each, without the privity of 

 the other, and that their answers thus obtained would enable us to 

 decide whether there was any material difference in their tastes, facul- 

 ties, and susceptibilities. 



