Which scientist first explained the dispersion of light?

$(a)$ Explain the following terms used in relation to defects of vision and corrections provided for them:
$(i)$ Myopia $(ii)$ Astigmatism $(iii)$ Bifocal lenses $(iv)$ Far-sightedness (Hypermetropia).
$(b)$ Describe with a ray diagram how a person with myopia can be helped by spectacles.

How will you use two identical prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light? Draw the diagram.

Give one example in nature where we can see the dispersion of white light.

Through which part of the eye do light rays from an object first enter the eye?

$(a)$ State the reasons which lead to hypermetropia. With the help of suitable diagrams,explain this defect of vision and its correction.
$(b)$ Draw a diagram of an experimental arrangement for observing the scattering of light in a colloidal solution. Name the two chemicals used in this activity.