\magnification=\magstep2

$$
\eqalign {
{\rm Flux\ F} &= {{\rm energy }\over{\rm (unit\ area) * (unit\ time)}} \cr
              &= {{ E }\over{ dA * dt}} \cr
}
$$

$$
{ F_{\lambda} d\lambda} = {{E_{\lambda} d\lambda }\over{dA * dt * d\lambda }} 
$$

$$
{I_{\lambda}} = {{E_{\lambda} d\lambda}\over 
                      {dA * dt * d\lambda * \cos\theta * d\Omega}}
$$

$$
{u_\lambda d\lambda} = {  {{1}\over{c}} {\int I_\lambda d\lambda d\Omega } }
$$

$$
{u_\lambda d\lambda} = {  {{4 \pi }\over{c}} I_\lambda d\lambda  }
$$



\vfill \eject


$$
{u_\lambda d\lambda} = {  {{8 \pi h c / {\lambda^5} }\over
                {e^{(hc / \lambda k T)} - 1 }} d\lambda  }
$$

$$
{u_\lambda d\lambda} = {  {{4 \sigma T^4 }\over{c}}  }
$$

$$
{ p } = { { E } \over {c} }
$$

$$
{ P_{rad} d\lambda } = {  {{1}\over{c}}  { \int I_\lambda d\lambda \cos^2\theta 
                  d\Omega } }
$$


$$
{ P_{rad} d\lambda } = {  {{4 \pi}\over{3 c}}   I_\lambda d\lambda   }
$$

$$
{ P_{rad} d\lambda } = {  {{4 \pi}\over{3 c}}  { \int {  B_\lambda (T) d\lambda   } } }
     =   {{4 \sigma T^4 }\over{3 c}}  =  {{1}\over{3}} u
$$


\bye
