A portal server keeps a record of the availability of portlets. The connector comprises at least one cell plate connector including a wall with a multiple spaced slots for receiving the lugs from either the positive or negative plates of the cells. 5NA\u2266NA1<NA NA1<n where NA1 is a numerical aperture derived from an angle made by a ray closest to the optical axis, of rays of light passing through the partial aperture, with the optical axis on the specimen, NA is the maximum numerical aperture of the objective lens, and n is the refractive index of a medium holding the specimen. The magnets extend in general alignment with the coils.