The electronic Raman scattering of both tetragonal ${\mathit{A}}_{1\mathit{g}}$ and ${\mathit{B}}_{1\mathit{g}}$ symmetries has been measured in ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{8+\mathrm{\delta }}$ single crystals as a function of the temperature. We observe that a redistribution of the electronic continuum spectrum below ${\mathit{T}}_{\mathit{c}}$ exhibits two aspects of the temperature dependence: One of them is associated with its energy scale, which has a significant temperature variation only just below ${\mathit{T}}_{\mathit{c}}$. This indicates an abrupt opening of the superconducting gap. The other is associated with the variation of the spectral weight, which shows a more gradual temperature dependence compared with the former. This indicates that a superconducting condensation of thermally excited quasiparticles occurs gradually with decreasing temperature. We also find that the ${\mathit{A}}_{1\mathit{g}}$ and ${\mathit{B}}_{1\mathit{g}}$ spectra exhibit a similar temperature dependence below ${\mathit{T}}_{\mathit{c}}$.

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