**Table 6:** Extinction in K (2.2 ${\rm ~ \mu m}$ ) calculated by (1) using Eq. (9), and (2) using the Br $\beta$ /Br $\alpha$ decrement observed by ISO (unless otherwise is indicated).
Source	$A_{\rm K}$ (1) $^\natural$		$A_{\rm K}$ (2)	Source	$A_{\rm K}$ (1) $^\natural$		$A_{\rm K}$ (2)
IRAS 01045	$3.2 \pm 1.4$	(1)	$\ddagger$	IRAS 17160	$5.6 \pm 0.3$	(1)	$5.8 \pm2.3^\star$
IRAS 10589	$1.3 \pm 0.1$	(4)	$1.5 \pm 0.5$	IRAS 17221	$1.8 \pm 0.2$	(2)	$1.8 \pm 0.4$
IRAS 11143	$0.8 \pm 0.1$	(2)	<0.6	IRAS 17279	$2.2 \pm 0.5$	(1)	$\ddagger$
IRAS 12063	$1.5 \pm 0.1$	(6)	$0.8\pm0.5$	IRAS 18032	$1.1 \pm 0.3$	(1)	$\ddagger$
IRAS 12073	$1.47 \pm 0.06$	(9)	$0.8\pm0.2$	IRAS 18479	$7.8 \pm 0.2$	(1)	$\ddagger$
IRAS 12331	$1.3 \pm 0.3$	(1)	$\ddagger$	IRAS 19442	<1.8		$\ddagger$
IRAS 15384	$1.53 \pm 0.09$	(6)	$1.3 \pm 0.3$	IRAS 19598	$2.49 \pm 0.05$	(9)	$1.6 \pm 0.2$
IRAS 15502	$3.1 \pm 0.2$	(3)	$2.7\pm0.6$	DR21	$2.6 \pm 0.3$	(1)	$3.1\pm0.7^\star$
IRAS 16128	$\Diamond$	(2)	$\rhd$	IRAS 23133	$0.4\pm0.1$	(2)	$\sim$ 0

$^\natural$ Given in brackets is the number of H I lines used in the calculation (see text). $^\ddagger$ Only Br $\alpha$ is available from the SWS spectrum. $^\Diamond$ Two lines (Br $\alpha$ and Br $\beta$ ) are observed by the ISO-SWS, but the $A_{\rm K}$ extinctions derived from them are very different ( $2.3 \pm 0.3$ and $0.8\pm0.2$ , respectively). $^\rhd$ The Br $\alpha$ /Br $\beta$ decrement is not consistent with a $\lambda^{-\alpha}$ law. $^\star$ Calculated using the Pf $\alpha$ /Br $\alpha$ decrement.

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