The researcher used a jar of beans to test conformity. Participants were asked to make individual estimates of the number of beans in the jar (this is actually quite hard to guess - my students have tried it and most people get it very wrong).
Then participants discussed the number in a group. All were in a state of ignorance, and therefore were open to the ideas of others. After discussing, each participant gave a revised individual estimate.
Jenness found that estimates had conformed towards a 'group norm' - even though nobody knew the right answer, there was apparently comfort in sticking close to others.
In real life, people often look to others if they don't know what to do - when travelling in an unfamiliar culture, for example, or if stuck on a school practical!
Jenness, A. (1932). The role of discussion in changing opinion regarding matter of fact. Journal of Abnormal and Social Psychology, 27, 279-296.
See also: Asch (1955)